[ Upstream commit d208261e9f ]
Our hardware registers are set through GCE, not by the CPU.
DRM might assume the hardware is disabled immediately after calling
atomic_disable() of drm_plane, but it is only truly disabled after the
GCE IRQ is triggered.
Additionally, the cursor plane in DRM uses async_commit, so DRM will
not wait for vblank and will free the buffer immediately after calling
atomic_disable().
To prevent the framebuffer from being freed before the layer disable
settings are configured into the hardware, which can cause an IOMMU
fault error, a wait_event_timeout has been added to wait for the
ddp_cmdq_cb() callback,indicating that the GCE IRQ has been triggered.
Fixes: 2f965be7f9 ("drm/mediatek: apply CMDQ control flow")
Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20250624113223.443274-1-jason-jh.lin@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 94c9337165 ]
When calling component_bind_all(), if a component that is included
in the list fails, all of those that have been successfully bound
will be unbound, but this driver has two components lists for two
actual devices, as in, each mmsys instance has its own components
list.
In case mmsys0 (or actually vdosys0) is able to bind all of its
components, but the secondary one fails, all of the components of
the first are kept bound, while the ones of mmsys1/vdosys1 are
correctly cleaned up.
This is not right because, in case of a failure, the components
are re-bound for all of the mmsys/vdosys instances without caring
about the ones that were previously left in a bound state.
Fix that by calling component_unbind_all() on all of the previous
component masters that succeeded binding all subdevices when any
of the other masters errors out.
Fixes: 1ef7ed4835 ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250403104741.71045-4-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 80805b62ea ]
In function mtk_drm_get_all_drm_priv(), this driver is incrementing
the refcount for the sub-drivers of mediatek-drm with a call to
device_find_child() when taking a reference to all of those child
devices.
When the component bind fails multiple times this results in a
refcount_t overflow, as the reference count is never decremented:
fix that by adding a call to put_device() for all of the mmsys
devices in a loop, in error cases of mtk_drm_bind() and in the
mtk_drm_unbind() callback.
Fixes: 1ef7ed4835 ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250403104741.71045-3-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 22918591fb ]
This driver is taking a kobject for mtk_mutex only once per mmsys
device for each drm-mediatek driver instance, differently from the
behavior with other components, but it is decrementing the kobj's
refcount in a loop and once per mmsys: this is not right and will
result in a refcount_t underflow warning when mediatek-drm returns
multiple probe deferrals in one boot (or when manually bound and
unbound).
Besides that, the refcount for mutex_dev was not decremented for
error cases in mtk_drm_bind(), causing another refcount_t warning
but this time for overflow, when the failure happens not during
driver bind but during component bind.
In order to fix one of the reasons why this is happening, remove
the put_device(xx->mutex_dev) loop from the mtk_drm_kms_init()'s
put_mutex_dev label (and drop the label) and add a single call to
correctly free the single incremented refcount of mutex_dev to
the mtk_drm_unbind() function to fix the refcount_t underflow.
Moreover, add the same call to the error cases in mtk_drm_bind()
to fix the refcount_t overflow.
Fixes: 1ef7ed4835 ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250403104741.71045-2-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 473c33f5ce ]
In preparation for adding support for MT8195's HDMI reserved
DPI, add calls to clk_prepare_enable() / clk_disable_unprepare()
for the TVD clock: in this particular case, the aforementioned
clock is not (and cannot be) parented to neither pixel or engine
clocks hence it won't get enabled automatically by the clock
framework.
Please note that on all of the currently supported MediaTek
platforms, the TVD clock is always a parent of either pixel or
engine clocks, and this means that the common clock framework
is already enabling this clock before the children.
On such platforms, this commit will only increase the refcount
of the TVD clock without any functional change.
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250217154836.108895-10-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 106a6de46c ]
The function mtk_dp_wait_hpd_asserted() may be called before the
`mtk_dp->drm_dev` pointer is assigned in mtk_dp_bridge_attach().
Specifically it can be called via this callpath:
- mtk_edp_wait_hpd_asserted
- [panel probe]
- dp_aux_ep_probe
Using "drm" level prints anywhere in this callpath causes a NULL
pointer dereference. Change the error message directly in
mtk_dp_wait_hpd_asserted() to dev_err() to avoid this. Also change the
error messages in mtk_dp_parse_capabilities(), which is called by
mtk_dp_wait_hpd_asserted().
While touching these prints, also add the error code to them to make
future debugging easier.
Fixes: 7eacba9a08 ("drm/mediatek: dp: Add .wait_hpd_asserted() for AUX bus")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250116094249.1.I29b0b621abb613ddc70ab4996426a3909e1aa75f@changeid/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit f8d9b91739 ]
Touching DISP_REG_OVL_PITCH_MSB leads to video overlay on MT2701, MT7623N
and probably other older SoCs being broken.
Move setting up AFBC layer configuration into a separate function only
being called on hardware which actually supports AFBC which restores the
behavior as it was before commit c410fa9b07 ("drm/mediatek: Add AFBC
support to Mediatek DRM driver") on non-AFBC hardware.
Fixes: c410fa9b07 ("drm/mediatek: Add AFBC support to Mediatek DRM driver")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: c7fbd3c3e6.1734397800.git.daniel@makrotopia.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 76aed5e00f ]
Registers DSI_VM_CMD and DSI_SHADOW_DEBUG start at different
addresses in both MT8186 and MT8188 compared to the older IPs.
Add two members in struct mtk_dsi_driver_data to specify the
offsets for these two registers on a per-SoC basis, then do
specify those in all of the currently present SoC driver data.
This fixes writes to the Video Mode Command Packet Control
register, fixing enablement of command packet transmission
(VM_CMD_EN) and allowance of this transmission during the
VFP period (TS_VFP_EN) on both MT8186 and MT8188.
Fixes: 03d7adc410 ("drm/mediatek: Add mt8186 dsi compatible to mtk_dsi.c")
Fixes: 814d5341f3 ("drm/mediatek: Add mt8188 dsi compatible to mtk_dsi.c")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241219112733.47907-1-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 0d68b55887 ]
Fix dp mode valid issue to avoid abnormal display of limit state.
After DP passes link training, it can express the lane count of the
current link status is good. Calculate the maximum bandwidth supported
by DP using the current lane count.
The color format will select the best one based on the bandwidth
requirements of the current timing mode. If the current timing mode
uses RGB and meets the DP link bandwidth requirements, RGB will be used.
If the timing mode uses RGB but does not meet the DP link bandwidthi
requirements, it will continue to check whether YUV422 meets
the DP link bandwidth.
FEC overhead is approximately 2.4% from DP 1.4a spec 2.2.1.4.2.
The down-spread amplitude shall either be disabled (0.0%) or up
to 0.5% from 1.4a 3.5.2.6. Add up to approximately 3% total overhead.
Because rate is already divided by 10,
mode->clock does not need to be multiplied by 10.
Fixes: f70ac097a2 ("drm/mediatek: Add MT8195 Embedded DisplayPort driver")
Signed-off-by: Liankun Yang <liankun.yang@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241025083036.8829-3-liankun.yang@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 924d66011f ]
The PHY portion of the mediatek hdmi driver was originally part of
the driver it self and later split out into drivers/phy, which a
'select' to keep the prior behavior.
However, this leads to build failures when the PHY driver cannot
be built:
WARNING: unmet direct dependencies detected for PHY_MTK_HDMI
Depends on [n]: (ARCH_MEDIATEK || COMPILE_TEST [=y]) && COMMON_CLK [=y] && OF [=y] && REGULATOR [=n]
Selected by [m]:
- DRM_MEDIATEK_HDMI [=m] && HAS_IOMEM [=y] && DRM [=m] && DRM_MEDIATEK [=m]
ERROR: modpost: "devm_regulator_register" [drivers/phy/mediatek/phy-mtk-hdmi-drv.ko] undefined!
ERROR: modpost: "rdev_get_drvdata" [drivers/phy/mediatek/phy-mtk-hdmi-drv.ko] undefined!
The best option here is to just not select the phy driver and leave that
up to the defconfig. Do the same for the other PHY and memory drivers
selected here as well for consistency.
Fixes: a481bf2f0c ("drm/mediatek: Separate mtk_hdmi_phy to an independent module")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241218085837.2670434-1-arnd@kernel.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit da03801ad0 ]
mtk_crtc_finish_page_flip() is used to notify userspace that a
page flip has been completed, allowing userspace to free the frame
buffer of the last frame and commit the next frame.
In MediaTek's hardware design for configuring display hardware by using
GCE, `DRM_EVENT_FLIP_COMPLETE` should be notified to userspace after
GCE has finished configuring all display hardware settings for each
atomic_commit().
Currently, mtk_crtc_finish_page_flip() cannot guarantee that GCE has
configured all the display hardware settings of the last frame.
Therefore, to increase the accuracy of the timing for notifying
`DRM_EVENT_FLIP_COMPLETE` to userspace, mtk_crtc_finish_page_flip()
should be moved to ddp_cmdq_cb().
Fixes: 7f82d9c438 ("drm/mediatek: Clear pending flag when cmdq packet is done")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241211034716.29241-1-jason-jh.lin@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
OVL_CON_CLRFMT_MAN is a configuration for extending color format
settings of DISP_REG_OVL_CON(n).
It will change some of the original color format settings.
Take the settings of (3 << 12) for example.
- If OVL_CON_CLRFMT_MAN = 0 means OVL_CON_CLRFMT_RGBA8888.
- If OVL_CON_CLRFMT_MAN = 1 means OVL_CON_CLRFMT_PARGB8888.
Since previous SoCs did not support OVL_CON_CLRFMT_MAN, this means
that the SoC does not support the premultiplied color format.
It will break the original color format setting of MT8173.
Therefore, the blend_modes is added to the driver data and then
mtk_ovl_fmt_convert() will check the blend_modes to see if
pre-multiplied is supported in the current platform.
If it is not supported, use coverage mode to set it to the supported
color formats to solve the degradation problem.
Fixes: a3f7f7ef4b ("drm/mediatek: Support "Pre-multiplied" blending in OVL")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241009034646.13143-5-jason-jh.lin@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
OVL_CON_AEN is for alpha blending enable.
For the SoC that is supported the blend_modes, OVL_CON_AEN will always
enabled to use constant alpha and then use the ignore_pixel_alpha bit
to do the alpha blending for XRGB8888 format.
Note that ignore pixel alpha bit is not supported if the SoC is not
supported the blend_modes.
So it will break the original setting of XRGB8888 format for the
blend_modes unsupported SoCs, such as MT8173.
To fix the downgrade issue, enable alpha blending only when a valid
blend_mode or has_alpha is set.
Fixes: bc46eb5d5d ("drm/mediatek: Support DRM plane alpha in OVL")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241009034646.13143-2-jason-jh.lin@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Pull dma-mapping updates from Christoph Hellwig:
- support DMA zones for arm64 systems where memory starts at > 4GB
(Baruch Siach, Catalin Marinas)
- support direct calls into dma-iommu and thus obsolete dma_map_ops for
many common configurations (Leon Romanovsky)
- add DMA-API tracing (Sean Anderson)
- remove the not very useful return value from various dma_set_* APIs
(Christoph Hellwig)
- misc cleanups and minor optimizations (Chen Y, Yosry Ahmed, Christoph
Hellwig)
* tag 'dma-mapping-6.12-2024-09-19' of git://git.infradead.org/users/hch/dma-mapping:
dma-mapping: reflow dma_supported
dma-mapping: reliably inform about DMA support for IOMMU
dma-mapping: add tracing for dma-mapping API calls
dma-mapping: use IOMMU DMA calls for common alloc/free page calls
dma-direct: optimize page freeing when it is not addressable
dma-mapping: clearly mark DMA ops as an architecture feature
vdpa_sim: don't select DMA_OPS
arm64: mm: keep low RAM dma zone
dma-mapping: don't return errors from dma_set_max_seg_size
dma-mapping: don't return errors from dma_set_seg_boundary
dma-mapping: don't return errors from dma_set_min_align_mask
scsi: check that busses support the DMA API before setting dma parameters
arm64: mm: fix DMA zone when dma-ranges is missing
dma-mapping: direct calls for dma-iommu
dma-mapping: call ->unmap_page and ->unmap_sg unconditionally
arm64: support DMA zone above 4GB
dma-mapping: replace zone_dma_bits by zone_dma_limit
dma-mapping: use bit masking to check VM_DMA_COHERENT
Thomas needs 5a498d4d06 ("drm/fbdev-dma: Only install deferred I/O
if necessary") in drm-misc, so start the backmerge cascade.
Signed-off-by: Simona Vetter <simona.vetter@ffwll.ch>
Mediatek DRM Next for Linux 6.12
1. Support alpha blending
2. Remove cl in struct cmdq_pkt
3. Fixup for ovl adaptor
4. Declare Z Position for all planes
5. Drop unnecessary check for property presence
6. Add dsi per-frame lp code for mt8188
7. Fix missing configuration flags in mtk_crtc_ddp_config()
8. Use spin_lock_irqsave() for CRTC event lock
9. Add power domain binding to the mediatek DPI controller
Signed-off-by: Dave Airlie <airlied@redhat.com>
From: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240901131354.2686-1-chunkuang.hu@kernel.org
In mtk_crtc_ddp_config(), mtk_crtc will use some configuration flags to
generate instructions to cmdq_handle, such as:
state->pending_config
mtk_crtc->pending_planes
plane_state->pending.config
mtk_crtc->pending_async_planes
plane_state->pending.async_config
These configuration flags may be set to false when a GCE IRQ comes calling
ddp_cmdq_cb(). This may result in missing prepare instructions,
especially if mtk_crtc_update_config() with the flase need_vblank (no need
to wait for vblank) cases.
Therefore, the mtk_crtc->config_updating flag is set at the beginning of
mtk_crtc_update_config() to ensure that these configuration flags won't be
changed when the mtk_crtc_ddp_config() is preparing instructions.
But somehow the ddp_cmdq_cb() didn't use the mtk_crtc->config_updating
flag to prevent those pending config flags from being cleared.
To avoid missing the configuration when generating the config instruction,
the config_updating flag should be added into ddp_cmdq_cb() and be
protected with spin_lock.
Fixes: 7f82d9c438 ("drm/mediatek: Clear pending flag when cmdq packet is done")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Fei Shao <fshao@chromium.org>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240827-drm-fixup-0819-v3-1-4761005211ec@mediatek.com/
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240827-drm-fixup-0819-v3-2-4761005211ec@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Adding the per-frame lp function of mt8188, which can keep HFP in HS and
reduce the time required for each line to enter and exit low power.
Per Frame LP:
|<----------One Active Frame-------->|
--______________________________________----___________________
^HSA+HBP^^RGB^^HFP^^HSA+HBP^^RGB^^HFP^ ^HSA+HBP^^RGB^^HFP^
Per Line LP:
|<---------------One Active Frame----------->|
--______________--______________--______________----______________
^HSA+HBP^^RGB^ ^HSA+HBP^^RGB^ ^HSA+HBP^^RGB^ ^HSA+HBP^^RGB^
Signed-off-by: Shuijing Li <shuijing.li@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240826060654.24038-1-shuijing.li@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
of_property_read_u32() returns -EINVAL if a property is not present, so
the preceding check for presence with of_find_property() can be
dropped. Really, what the errno is shouldn't matter. Either the property
can be read and used or it can't and is ignored.
This is part of a larger effort to remove callers of of_find_property()
and similar functions. of_find_property() leaks the DT struct property
and data pointers which is a problem for dynamically allocated nodes
which may be freed.
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240731201407.1838385-1-robh@kernel.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
MediaTek SoCs support multiple planes, one of which is the primary
and all the others are overlays (and CURSOR is the last overlay).
In all currently supported SoCs, the Z order of the overlays can't
be changed with any fast muxing action, and can only be changed by
swapping the contents of the entire register set of one overlay
with the other to internally reorder the layer properties, which
is indeed feasible, but probably more expensive than desired.
Declare the Z position for all planes with an immutable property
at least for now, so that the userspace can take its decisions
accordingly.
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Fei Shao <fshao@chromium.org>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240718082507.216764-1-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
A NULL dev->dma_parms indicates either a bus that is not DMA capable or
grave bug in the implementation of the bus code.
There isn't much the driver can do in terms of error handling for either
case, so just warn and continue as DMA operations will fail anyway.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org> # For MMC
For some client driver, it want to reduce latency between excuting
previous packet command and next packet command, so append jump
command to the end of previous packet and the jump destination
address is the start address of next packet command buffer. Before
next packet exist, the previous packet has no information of where
to jump to, so append nop command first. When next packet exist,
change nop command to jump command. For mediatek drm driver, it
never has next packet, so appending nop command is redundant.
Because cmdq_pkt_finalize() would append nop command, so change
calling cmdq_pkt_finalize() to cmdq_pkt_eoc() to prevent append
redundant nop command.
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240810090918.7457-2-chunkuang.hu@kernel.org/
Support "Pre-multiplied" and "None" blend mode on MediaTek's chips by
adding correct blend mode property when the planes init.
Before this patch, only the "Coverage" mode (default) is supported.
For more information, there are three pixel blend modes in DRM driver:
"None", "Pre-multiplied", and "Coverage".
To understand the difference between these modes, let's take a look at
the following two approaches to do alpha blending:
1. Straight:
dst.RGB = src.RGB * src.A + dst.RGB * (1 - src.A)
This is straightforward and easy to understand, when the source layer is
compositing with the destination layer, it's alpha will affect the
result. This is also known as "post-multiplied", or "Coverage" mode.
2. Pre-multiplied:
dst.RGB = src.RGB + dst.RGB * (1 - src.A)
Since the source RGB have already multiplied its alpha, only destination
RGB need to multiply it. This is the "Pre-multiplied" mode in DRM.
For the "None" blend mode in DRM, it means the pixel alpha is ignored
when compositing the layers, only the constant alpha for the composited
layer will take effects.
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hsiao Chien Sung <shawn.sung@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240717-alpha-blending-v4-5-4b1c806c0749@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
