linux-kernel - Re: Latest randconfig build errors

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Date:	Sun, 14 Apr 2013 00:29:46 -0400
From:	Rob Clark <robdclark@...il.com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
Cc:	Tony Lindgren <tony@...mide.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	arm@...nel.org, linux-omap <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Latest randconfig build errors

On Sat, Apr 13, 2013 at 5:45 PM, Thierry Reding
<thierry.reding@...onic-design.de> wrote:
> On Sat, Apr 13, 2013 at 08:54:22AM -0400, Rob Clark wrote:
>> On Mon, Mar 4, 2013 at 1:46 PM, Tony Lindgren <tony@...mide.com> wrote:
>> >
>> >> drivers/gpu/drm/tilcdc/tilcdc_slave.o:(.data+0x54): multiple definition of `__mod_of_device_table'
>> >> drivers/gpu/drm/tilcdc/tilcdc_tfp410.o:(.data+0x54): first defined here
>> >> drivers/gpu/drm/tilcdc/tilcdc_panel.o:(.data+0x54): multiple definition of `__mod_of_device_table'
>> >> drivers/gpu/drm/tilcdc/tilcdc_tfp410.o:(.data+0x54): first defined here
>> >> drivers/gpu/drm/tilcdc/tilcdc_drv.o:(.data+0x184): multiple definition of `__mod_of_device_table'
>> >> drivers/gpu/drm/tilcdc/tilcdc_tfp410.o:(.data+0x54): first defined here
>> >
>> > Rob, I assume you'll do a patch for this one?
>>
>>
>> oh, I apologize for the late reply, I didn't see this email...
>>
>> There is a patch that we can merge to make tilcdc bool instead of
>> tristate[1], which I suppose is ok for a temporary fix.  Although I'm
>> all-ears if someone has a better idea about how to fix this.  The
>> problem is that we have multiple sub-devices for different possible
>> panel drivers, so that depending on DT tables, the correct ones get
>> loaded for the hw.  But they are all built into a single module.
>> Splitting them into multiple modules will be problematic, as panel
>> drivers which are present really need to get probed before the
>> toplevel drm device..
>
> You could look at the Tegra driver. I had to solve a similar problem
> there. What I did is basically parse the DT in the host1x driver and add
> all device nodes which are required by DRM to a list. Later when the
> individual devices are probed they are removed from that list, so that
> when the list becomes empty we are sure that all required devices are
> there and only then call the drm_platform_init() function.

thx, ok, I'll have a look at this

> This fits very well with how Tegra hardware is designed because host1x
> is the parent for all DRM subdevices (DC, RGB/LVDS, HDMI, ...). So it is
> probed before any of its children and it can easily parse the DT upfront
> and initialize the list of required devices.
>
>> I suppose in theory it is possible to make drm
>> cope better with dynamically loaded outputs, but I'm not sure that
>> there is any way to do this without breaking userspace which expects
>> that all of the connectors/encoders are present once the drm device is
>> loaded.
>
> I had been thinking about this on and off for a while, but I haven't
> come up with anything concrete. Ideally we could just have some kind of
> event that userspace would listen for, so that new outputs can be
> dynamically added and userspace informed about them. Last time I checked
> most of the helpers assumed that the complete output configuration is
> known when the DRM device is registered, so some major rework will be
> required to efficiently make use of such dynamicity.

I'm less worried about the kernel re-work.. more worried about the
fact that we have no way to know whether userspace knows to listen for
this new event.  So anything down this path could, I think, be
considered as breaking userspace.

I think in the end, we need some way to have sort of "dummy"
connectors for output drivers which might or might not be probed, so
that from userspace perspective, non-present panels appear as displays
that are not plugged in.

BR,
-R


> Thierry
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