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coresight: etm4x: Add context synchronization before enabling trace

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According to the software usage PKLXF in Arm ARM (ARM DDI 0487 L.a), a
Context synchronization event is required before enabling the trace
unit.

An ISB is added to meet this requirement, particularly for guarding the
operations in the flow:

  etm4x_allow_trace()
   `> kvm_tracing_set_el1_configuration()
	`> write_sysreg_s(trfcr_while_in_guest, SYS_TRFCR_EL12)

Improved the barrier comments to provide more accurate information.

Fixes: 1ab3bb9df5 ("coresight: etm4x: Add necessary synchronization for sysreg access")
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Yeoreun Yun <yeoreum.yun@arm.com>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20251111-arm_coresight_power_management_fix-v6-5-f55553b6c8b3@arm.com
This commit is contained in:
Leo Yan
2025-11-11 18:58:39 +00:00
committed by Suzuki K Poulose
parent 4dc4e22f95
commit 64eb04ae54
1 changed files with 23 additions and 4 deletions
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27
drivers/hwtracing/coresight/coresight-etm4x-core.c
View File

@@ -446,10 +446,24 @@ static int etm4_enable_trace_unit(struct etmv4_drvdata *drvdata)
etm4x_relaxed_write32(csa, TRCRSR_TA, TRCRSR);
etm4x_allow_trace(drvdata);
/*
* According to software usage PKLXF in Arm ARM (ARM DDI 0487 L.a),
* execute a Context synchronization event to guarantee the trace unit
* will observe the new values of the System registers.
*/
if (!csa->io_mem)
isb();
/* Enable the trace unit */
etm4x_relaxed_write32(csa, 1, TRCPRGCTLR);
/* Synchronize the register updates for sysreg access */
/*
* As recommended by section 4.3.7 ("Synchronization when using system
* instructions to progrom the trace unit") of ARM IHI 0064H.b, the
* self-hosted trace analyzer must perform a Context synchronization
* event between writing to the TRCPRGCTLR and reading the TRCSTATR.
*/
if (!csa->io_mem)
isb();
@@ -931,11 +945,16 @@ static void etm4_disable_trace_unit(struct etmv4_drvdata *drvdata)
*/
etm4x_prohibit_trace(drvdata);
/*
* Make sure everything completes before disabling, as recommended
* by section 7.3.77 ("TRCVICTLR, ViewInst Main Control Register,
* SSTATUS") of ARM IHI 0064D
* Prevent being speculative at the point of disabling the trace unit,
* as recommended by section 7.3.77 ("TRCVICTLR, ViewInst Main Control
* Register, SSTATUS") of ARM IHI 0064D
*/
dsb(sy);
/*
* According to software usage VKHHY in Arm ARM (ARM DDI 0487 L.a),
* execute a Context synchronization event to guarantee no new
* program-flow trace is generated.
*/
isb();
/* Trace synchronization barrier, is a nop if not supported */
tsb_csync();