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

From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Alban <albeu@free.fr>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	linux-mtd@lists.infradead.org,
	Cyrille Pitchen <cyrille.pitchen@atmel.com>,
	Richard Weinberger <richard@nod.at>,
	Marek Vasut <marek.vasut@gmail.com>,
	Brian Norris <computersforpeace@gmail.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Rob Herring <robh+dt@kernel.org>,
	Maxime Ripard <maxime.ripard@free-electrons.com>,
	Moritz Fischer <moritz.fischer@ettus.com>
Subject: Re: [PATCH 2/3] mtd: Add support for reading MTD devices via the nvmem API
Date: Fri, 3 Mar 2017 13:34:19 +0100	[thread overview]
Message-ID: <20170303133419.2383dbce@bbrezillon> (raw)
In-Reply-To: <b2df74bb-dd86-bac1-ab8b-cbff6ca29b6f@linaro.org>

On Fri, 3 Mar 2017 11:23:16 +0000
Srinivas Kandagatla <srinivas.kandagatla@linaro.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.