linux-kernel - Re: [PATCH 2/3] mtd: Add support for reading MTD devices via the nvmem API

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Date:   Fri, 3 Mar 2017 14:30:21 +0100
From:   Alban <albeu@...e.fr>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Aban Bedel <albeu@...e.fr>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-mtd@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Richard Weinberger <richard@....at>,
        Marek Vasut <marek.vasut@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Moritz Fischer <moritz.fischer@...us.com>
Subject: Re: [PATCH 2/3] mtd: Add support for reading MTD devices via the
 nvmem API

On Fri, 3 Mar 2017 13:34:19 +0100
Boris Brezillon <boris.brezillon@...e-electrons.com> wrote:

> On Fri, 3 Mar 2017 11:23:16 +0000
> Srinivas Kandagatla <srinivas.kandagatla@...aro.org> wrote:
> 
> 
> >   
> > > +	mutex_lock(&mtd_nvmem_list_lock);
> > > +	list_for_each_entry(mtd_nvmem, &mtd_nvmem_list, list) {
> > > +		if (mtd_nvmem->mtd == mtd) {
> > > +			list_del(&mtd_nvmem->list);
> > > +			found = true;
> > > +			break;
> > > +		}
> > > +	}
> > > +	mutex_unlock(&mtd_nvmem_list_lock);
> > > +
> > > +	if (found) {
> > > +		if (nvmem_unregister(mtd_nvmem->nvmem))
> > > +			dev_err(&mtd->dev,
> > > +				"Failed to unregister NVMEM device\n");    
> > 
> > I will be nice to feedback error to top layer, as it does not make sense 
> > to remove providers if there are active consumers using it.
> > 
> > del_mtd_device(), unregister_mtd_user() have return values, I see no 
> > reason why notifiers  should not return errors.
> > May be if we should fix the remove() call backs to handle and return errors.  
> 
> It's more complicated than that. What should you do if one of the
> ->remove() notifier in the middle of the list is returning an error?  
> Some of them have already taken the remove notification into account.
> Should we call ->add() back on those notifiers? Also, I'm not sure they
> are all safe against double ->remove() calls, so if we might be in
> trouble when the removal is retried.

Re-adding make no sense as that could also fails. Keep it simple,
remove the notifier from the list when remove() succeed, abort when one
fails. In such a scenario that mean there is a dependency, the sys
admin should then solve this dependency and re-trigger the MTD removal.

Alban

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