linux-kernel - [PATCH 1/1] coresight: Fix TRCCONFIGR.QE sysfs interface

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Message-Id: <20220114173254.1876151-2-james.clark@arm.com>
Date:   Fri, 14 Jan 2022 17:32:54 +0000
From:   James Clark <james.clark@....com>
To:     mathieu.poirier@...aro.org, coresight@...ts.linaro.org
Cc:     suzuki.poulose@....com, James Clark <james.clark@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] coresight: Fix TRCCONFIGR.QE sysfs interface

It's impossible to program a valid value for TRCCONFIGR.QE
when TRCIDR0.QSUPP==0b10. In that case the following is true:

  Q element support is implemented, and only supports Q elements without
  instruction counts. TRCCONFIGR.QE can only take the values 0b00 or 0b11.

Currently the low bit of QSUPP is checked to see if the low bit of QE can
be written to, but as you can see when QSUPP==0b10 the low bit is cleared
making it impossible to ever write the only valid value of 0b11 to QE.
0b10 would be written instead, which is a reserved QE value even for all
values of QSUPP.

The fix is to allow writing the low bit of QE for any non zero value of
QSUPP.

This change doesn't go any further to validate if the user supplied value
is valid, because none of the other parts this function do, but it does fix
the case where it was impossible to ever set a valid value.

Signed-off-by: James Clark <james.clark@....com>
---
 drivers/hwtracing/coresight/coresight-etm4x-sysfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
index a0640fa5c55b..a99bb537ea23 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
@@ -368,7 +368,7 @@ static ssize_t mode_store(struct device *dev,
 	/* start by clearing QE bits */
 	config->cfg &= ~(BIT(13) | BIT(14));
 	/* if supported, Q elements with instruction counts are enabled */
-	if ((mode & BIT(0)) && (drvdata->q_support & BIT(0)))
+	if ((mode & BIT(0)) && drvdata->q_support)
 		config->cfg |= BIT(13);
 	/*
 	 * if supported, Q elements with and without instruction
-- 
2.17.1