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

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Date:   Wed, 27 Jan 2021 10:43:40 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Leo Yan <leo.yan@...aro.org>,
        Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH v2] coresight: etm4x: Handle accesses to TRCSTALLCTLR

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: stable@...r.kernel.org
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....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 think option 1 is best.

Thanks,
Mathieu

>  	spin_lock(&drvdata->spinlock);
>  	config->mode = val & ETMv4_MODE_ALL;
>  
> -- 
> 2.24.1
>