linux-kernel - Re: [PATCH v3 11/14] remoteproc: Deal with synchronisation when changing FW image

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Date:   Tue, 5 May 2020 18:27:48 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     ohad@...ery.com, loic.pallardy@...com, arnaud.pouliquen@...com,
        s-anna@...com, linux-remoteproc@...r.kernel.org, corbet@....net,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 11/14] remoteproc: Deal with synchronisation when
 changing FW image

On Fri 24 Apr 13:01 PDT 2020, Mathieu Poirier wrote:

> This patch prevents the firmware image from being displayed or changed
> when the remoteproc core is synchronising with a remote processor. This
> is needed since there is no guarantee about the nature of the firmware
> image that is loaded by the external entity.
> 
> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> ---
>  drivers/remoteproc/remoteproc_sysfs.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
> index 7f8536b73295..cdd322a6ecfa 100644
> --- a/drivers/remoteproc/remoteproc_sysfs.c
> +++ b/drivers/remoteproc/remoteproc_sysfs.c
> @@ -13,9 +13,20 @@
>  static ssize_t firmware_show(struct device *dev, struct device_attribute *attr,
>  			  char *buf)
>  {
> +	ssize_t ret;
>  	struct rproc *rproc = to_rproc(dev);
>  
> -	return sprintf(buf, "%s\n", rproc->firmware);
> +	/*
> +	 * In most instances there is no guarantee about the firmware
> +	 * that was loaded by the external entity.  As such simply don't
> +	 * print anything.

Not only "in most instances", we have no idea what firmware is running,
so this can be shortened.

However, this does implicate that on_init = true, after_crash = false,
this will read blank, but a future rproc_report_crash() will indeed load
and boot rproc->firmware.

> +	 */
> +	if (rproc_needs_syncing(rproc))
> +		ret = sprintf(buf, "\n");
> +	else
> +		ret = sprintf(buf, "%s\n", rproc->firmware);
> +
> +	return ret;
>  }
>  
>  /* Change firmware name via sysfs */
> @@ -39,6 +50,17 @@ static ssize_t firmware_store(struct device *dev,
>  		goto out;
>  	}
>  
> +	/*
> +	 * There is no point in trying to change the firmware if loading the
> +	 * image of the remote processor is done by another entity.
> +	 */
> +	if (rproc_needs_syncing(rproc)) {
> +		dev_err(dev,
> +			"can't change firmware while synchronising with MCU\n");

The conditional checks for a future event, but the error message
indicates an ongoing event. How about "can't change firmware on remote
controlled remote processor"? "externally controlled"?

Regards,
Bjorn

> +		err = -EBUSY;
> +		goto out;
> +	}
> +
>  	len = strcspn(buf, "\n");
>  	if (!len) {
>  		dev_err(dev, "can't provide a NULL firmware\n");
> -- 
> 2.20.1
>