Re: [PATCH v2 15/17] remoteproc: Correctly deal with MCU synchronisation when changing FW image

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Tue, Mar 31, 2020 at 05:14:18PM -0500, Suman Anna wrote:
> Hi Mathieu,
> 
> On 3/30/20 6:21 PM, Mathieu Poirier wrote:
> > On Fri, Mar 27, 2020 at 01:50:18PM +0000, Loic PALLARDY wrote:
> >>
> >>> This patch prevents the firmware image from being displayed or changed
> >>> when
> >>> the remoteproc core is synchronising with an MCU. 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@linaro.org>
> >>> ---
> >>>  drivers/remoteproc/remoteproc_sysfs.c | 25
> >>> ++++++++++++++++++++++++-
> >>>  1 file changed, 24 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/remoteproc/remoteproc_sysfs.c
> >>> b/drivers/remoteproc/remoteproc_sysfs.c
> >>> index 7f8536b73295..4956577ad4b4 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.
> >>> +	 */
> >>> +	if (rproc_sync_with_mcu(rproc))
> >>> +		ret = sprintf(buf, "\n");
> >> Is it enough to provide empty name, or should we add a message to indicate that's name is unkown/undefined ?
> >>
> > 
> > Don't know... It is easy to find plenty of cases in sysfs where null values are
> > represented with a "\n", and just as many where "unknown", "undefined" or "-1"
> > are used. I know GKH prefers the least amount of information as possible, hence
> > going with a "\n".
> > 
> > Again, no strong opinion...
> > 
> >> Regards,
> >> Loic
> >>> +	else
> >>> +		ret = sprintf(buf, "%s\n", rproc->firmware);
> >>> +
> >>> +	return ret;
> >>>  }
> >>>
> >>>  /* Change firmware name via sysfs */
> >>> @@ -33,6 +44,18 @@ static ssize_t firmware_store(struct device *dev,
> >>>  		return -EINVAL;
> >>>  	}
> >>>
> >>> +	/*
> >>> +	 * There is no point in trying to change the firmware if the MCU
> >>> +	 * is currently running or if loading of the image is done by
> >>> +	 * another entity.
> >>> +	 */
> >>> +	if (rproc_sync_with_mcu(rproc)) {
> >>> +		dev_err(dev,
> >>> +			"can't change firmware while synchronising with
> >>> MCU\n");
> >>> +		err = -EBUSY;
> >>> +		goto out;
> >>> +	}
> >>> +
> 
> So, I have done a patch sometime back to deny sysfs operations [1] (the
> primary usecase is for a rproc-client driver driven boot where auto-boot
> is not set) which is still a need for me. Do you see that as orthogonal
> to that, or can we leverage that here somehow. I cannot use the sync_
> conditions for my cases since they are not already booted before.

I will look at your patch and see if I there is a way to fit that in.  I will
get back to you...

> 
> Also, any reason why you want to do this check before the rproc->state
> unlike the logic around the 'state' file in the next patch?

No specific reason, I will move the check down to be consistent.

> 
> [1] https://patchwork.kernel.org/patch/10601325/
> 
> regards
> Suman
> 
> >>>  	if (rproc->state != RPROC_OFFLINE) {
> >>>  		dev_err(dev, "can't change firmware while running\n");
> >>>  		err = -EBUSY;
> >>> --
> >>> 2.20.1
> >>
>