linux-kernel - Re: [PATCH v2 1/2] media: ir-kbd-i2c: convert to i2c_new_dummy

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Date:   Sun, 4 Aug 2019 03:57:29 +0100
From:   Sean Young <sean@...s.org>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-i2c@...r.kernel.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] media: ir-kbd-i2c: convert to
 i2c_new_dummy_device()

On Sat, Aug 03, 2019 at 01:17:49PM -0300, Mauro Carvalho Chehab wrote:
> Em Tue, 30 Jul 2019 19:55:54 +0200
> Wolfram Sang <wsa+renesas@...g-engineering.com> escreveu:
> 
> > Convert this driver to use the new i2c_new_dummy_device() call and bail
> > out if the dummy device cannot be registered to make failure more
> > visible to the user.
> > 
> 
> Please don't do that.
> 
> At first glance, devm_* sounds a good idea, but we had enough issues
> using it on media system.
> 
> I don't mind mind much if some SoC specific would use it, but doing
> it on generic drivers is a very bad idea. We have removed almost all
> devm_* calls from the media system.
> 
> The problem with devm is that it the de-allocation routines aren't
> called during device unbind. They happen a way later, only when the
> device itself is physically removed, or the driver is removed.

Yes, good point.

> That caused lots of headaches to debug memory lifetime issues on
> media.

Indeed this becomes much more complex. Explicit freeing is much better.


Thanks,
Sean