linux-kernel - Re: [RFC PATCH 01/14] coresight: etm4x: Skip save/restore before device registration

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Date:   Wed, 29 Jul 2020 12:01:28 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mike.leach@...aro.org, coresight@...ts.linaro.org
Subject: Re: [RFC PATCH 01/14] coresight: etm4x: Skip save/restore before
 device registration

Hi Suzuki,

I have starte to review this - comments will be scattered over a few days.

On Wed, Jul 22, 2020 at 06:20:27PM +0100, Suzuki K Poulose wrote:
> Skip cpu save/restore before the coresight device is registered.
> 
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  drivers/hwtracing/coresight/coresight-etm4x.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> index 6d7d2169bfb2..cb83fb77ded6 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> @@ -1135,7 +1135,13 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
>  {
>  	int i, ret = 0;
>  	struct etmv4_save_state *state;
> -	struct device *etm_dev = &drvdata->csdev->dev;
> +	struct coresight_device *csdev = drvdata->csdev;
> +	struct device *etm_dev;
> +
> +	if (WARN_ON(!csdev))
> +		return -ENODEV;
> +
> +	etm_dev = &csdev->dev;
>  
>  	/*
>  	 * As recommended by 3.4.1 ("The procedure when powering down the PE")
> @@ -1261,6 +1267,10 @@ static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
>  {
>  	int i;
>  	struct etmv4_save_state *state = drvdata->save_state;
> +	struct coresight_device *csdev = drvdata->csdev;
> +
> +	if (WARN_ON(!csdev))
> +		return;

Restore and save operations are only called from etm4_cpu_pm_notify() where the
check for a valid drvdata->csdev is already done.

>  
>  	CS_UNLOCK(drvdata->base);
>  
> @@ -1368,6 +1378,10 @@ static int etm4_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
>  
>  	drvdata = etmdrvdata[cpu];
>  
> +	/* If we have not registered the device there is nothing to do */
> +	if (!drvdata->csdev)
> +		return NOTIFY_OK;

Can you describe the scenario you've seen this happening in?  Probably best to
add it to the changelog. 

> +
>  	if (!drvdata->save_state)
>  		return NOTIFY_OK;
>  
> -- 
> 2.24.1
>