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coresight: etm4x: fix underflow for usage of (nrseqstate - 1)

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According to IHI006H Embedded Trace Macrocell Architecture
Specification[0], TRCSEQEVR<n> is implemented only when
TRCIDR5.NUMSEQSTATE is 0b100, in which case n ranges from 0 to 2;
otherwise, TRCIDR5.NUMSEQSTATE is 0b000.

IOW, the number of usage in the initialisation or setting
TRCSEQEVR<n> with drvdata->nrseqstate - 1 in the loop could make
underflow issue when TRCIDR5.NUMSEQSTATE is 0b000.

Therefore, introduce nr_seq_ctrls field and untie it from nrseqstate.
As part of this introduce ETM_MAX_SEQ_TRANSITIONS macro and
apply nr_seq_ctrls and above macro to TRCSEQEVR<n> relevant fields setup.

Link: https://developer.arm.com/documentation/ihi0064/latest/ [0]
Fixes: 2e1cdfe184 ("coresight-etm4x: Adding CoreSight ETM4x driver")
Suggested-by: Leo Yan <leo.yan@arm.com>
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260725113645.57519-3-yeoreum.yun@arm.com
This commit is contained in:
Yeoreum Yun 2026-07-25 12:36:34 +01:00 • committed by Suzuki K Poulose
commit 1674d9bff8
4 changed files with 16 additions and 8 deletions
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