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

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Message-ID: <20121031085047.GE1835@avionic-0098.mockup.avionic-design.de>
Date:	Wed, 31 Oct 2012 09:50:47 +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 Wed, Oct 31, 2012 at 09:31:27AM +0100, Laurent Pinchart wrote:
> Hi Thierry,
> 
> On Wednesday 31 October 2012 09:26:07 Thierry Reding wrote:
> > On Fri, Oct 26, 2012 at 04:06:27PM +0200, Laurent Pinchart wrote:
> > > 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.
> 
> So we either need your patch, or a documentation update :-)
> 
> The patch itself is fine, I'll let others comment on the approach.

The patch already went in through David's tree, so I guess that says
much about his opinion on the matter. =) Still I think there's some
value in making this consistent across all drivers and if everybody
agrees I'll volunteer to write the patch.

Thierry

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