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

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Message-ID: <20200430203205.GA18004@xps15>
Date:   Thu, 30 Apr 2020 14:32:05 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaud POULIQUEN <arnaud.pouliquen@...com>
Cc:     bjorn.andersson@...aro.org, ohad@...ery.com, loic.pallardy@...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 Wed, Apr 29, 2020 at 10:52:48AM +0200, Arnaud POULIQUEN wrote:
> 
> 
> On 4/24/20 10:01 PM, 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.
> > +	 */
> > +	if (rproc_needs_syncing(rproc))
> > +		ret = sprintf(buf, "\n");
> 
> A default name is provided in sysfs if no firmware is started/synchronised on boot.
> 
> IMO providing an empty name here could be confusing.
> Perhaps a refactoring of this sysfs entry would be nice:
>  - Normal boot (no firmware loaded) : empty name instead of a default name

That is guaranteed to break user space so we can't proceed this way.

>  - auto_boot: name provided by the platform driver or default name ( current implementation)
>  - synchronization: a predefined name such as Default, unknown, External, None,...   

Loic had the same comment.  Usually it is best to provide sysfs output that
don't need parsing, i.e 0/1 or nothing at all, but in the remoteproc subsystem
we already have "state", "name" and "firmware" that need parsing.  As such my
next revision will have "unknown", which I think is the best way to describe the
situation.

> 
> > +	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");
> 
> I don't know if you decide to keep "MCU" or not. If not the case
> you have also some other instances in your patch 9/14.

MCU should be long gone.  I thought I had spotted them all but was obviously
wrong.

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