linux-kernel - Re: [PATCH] drm: platform: Don't initialize driver-private data

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Message-ID: <20121031082607.GA1835@avionic-0098.mockup.avionic-design.de>
Date:	Wed, 31 Oct 2012 09:26:07 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: platform: Don't initialize driver-private data

On Fri, Oct 26, 2012 at 04:06:27PM +0200, Laurent Pinchart wrote:
> Hi Thierry,
> 
> Thank you for the patch, and sorry for the late reply.
> 
> On Monday 15 October 2012 20:03:42 Thierry Reding wrote:
> > Platform device drivers usually use the driver-private data for their
> > own purposes. Having it overwritten by drm_platform_init() is confusing
> > and error-prone.
> 
> If you want to push drivers that way, you should get rid of the 
> pci_set_drvdata() call in core DRM as well. This would push device driver data 
> handling down to all drivers, so I'm not convinced it would actually make 
> things simpler.

I think the problem doesn't exist for PCI-based DRM drivers, so I didn't
look at it. The issue only arises once the DRM needs to glue together
multiple devices, as is usual with the drivers for embedded devices,
where the drivers are based on platform devices.

I agree, though, that for consistency it would be nicer not to do this
for the PCI-based DRM drivers either. If David agrees I can take a look
at converting the other drivers along with the change to the DRM core.

Pushing the handling of the driver-private data down to the drivers may
not make things easier, but at least it would be consistent with other
drivers. I didn't mention this in the patch description but it actually
took me a day to track down why the driver kept crashing until I figured
out that drm_platform_init() actually modified the pointer.

Thierry

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