Re: [PATCH v2] coresight: etm4x: Handle accesses to TRCSTALLCTLR

[Suzuki K Poulose]

On 1/27/21 5:43 PM, Mathieu Poirier wrote:

Good day,

On Wed, Jan 27, 2021 at 12:00:32PM +0000, Suzuki K Poulose wrote:

TRCSTALLCTLR register is only implemented if

    TRCIDR3.STALLCTL == 0b1

Make sure the driver touches the register only it is implemented.

Cc: sta...@vger.kernel.org
Cc: Mathieu Poirier <mathieu.poir...@linaro.org>
Cc: Leo Yan <leo....@linaro.org>
Cc: Mike Leach <mike.le...@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
---
Changes since v1:
   - No change to the patch, fixed the stable email address and
     added usual reviewers.
---
  drivers/hwtracing/coresight/coresight-etm4x-core.c  | 9 ++++++---
  drivers/hwtracing/coresight/coresight-etm4x-sysfs.c | 3 +++
  2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c 
b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index b40e3c2bf818..814b49dae0c7 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -367,7 +367,8 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
        etm4x_relaxed_write32(csa, 0x0, TRCAUXCTLR);
        etm4x_relaxed_write32(csa, config->eventctrl0, TRCEVENTCTL0R);
        etm4x_relaxed_write32(csa, config->eventctrl1, TRCEVENTCTL1R);
-       etm4x_relaxed_write32(csa, config->stall_ctrl, TRCSTALLCTLR);
+       if (drvdata->stallctl)
+               etm4x_relaxed_write32(csa, config->stall_ctrl, TRCSTALLCTLR);
        etm4x_relaxed_write32(csa, config->ts_ctrl, TRCTSCTLR);
        etm4x_relaxed_write32(csa, config->syncfreq, TRCSYNCPR);
        etm4x_relaxed_write32(csa, config->ccctlr, TRCCCCTLR);
@@ -1545,7 +1546,8 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
        state->trcauxctlr = etm4x_read32(csa, TRCAUXCTLR);
        state->trceventctl0r = etm4x_read32(csa, TRCEVENTCTL0R);
        state->trceventctl1r = etm4x_read32(csa, TRCEVENTCTL1R);
-       state->trcstallctlr = etm4x_read32(csa, TRCSTALLCTLR);
+       if (drvdata->stallctl)
+               state->trcstallctlr = etm4x_read32(csa, TRCSTALLCTLR);
        state->trctsctlr = etm4x_read32(csa, TRCTSCTLR);
        state->trcsyncpr = etm4x_read32(csa, TRCSYNCPR);
        state->trcccctlr = etm4x_read32(csa, TRCCCCTLR);
@@ -1657,7 +1659,8 @@ static void etm4_cpu_restore(struct etmv4_drvdata 
*drvdata)
        etm4x_relaxed_write32(csa, state->trcauxctlr, TRCAUXCTLR);
        etm4x_relaxed_write32(csa, state->trceventctl0r, TRCEVENTCTL0R);
        etm4x_relaxed_write32(csa, state->trceventctl1r, TRCEVENTCTL1R);
-       etm4x_relaxed_write32(csa, state->trcstallctlr, TRCSTALLCTLR);
+       if (drvdata->stallctl)
+               etm4x_relaxed_write32(csa, state->trcstallctlr, TRCSTALLCTLR);
        etm4x_relaxed_write32(csa, state->trctsctlr, TRCTSCTLR);
        etm4x_relaxed_write32(csa, state->trcsyncpr, TRCSYNCPR);
        etm4x_relaxed_write32(csa, state->trcccctlr, TRCCCCTLR);
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c 
b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
index 1c490bcef3ad..cd9249fbf913 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
@@ -296,6 +296,9 @@ static ssize_t mode_store(struct device *dev,
        if (kstrtoul(buf, 16, &val))
                return -EINVAL;

+ if ((val & ETM_MODE_ISTALL_EN) && !drvdata->stallctl)

+               return -EINVAL;
+

We have two choices here:

1) Follow what is already done in this function for implementation define
options like ETM_MODE_BB, ETMv4_MODE_CTXID, ETM_MODE_RETURNSTACK and others.  In
that case we would have:

         /* bit[8], Instruction stall bit */
         if ((config->mode & ETM_MODE_ISTALL_EN) && drvdata->stallctl == true))
                 config->stall_ctrl |= BIT(8);
         else
                 config->stall_ctrl &= ~BIT(8);

2) Return -EINVAL when something is not supported, like you have above.  In that
case we'd have to enact the same behavior for all the options, which has the > 
potential of breaking user space.

I did think about this and but now I agree  1 is better for now. I will respin.


Cheers
Suzuki