linux-kernel - Re: [PATCH 3/5] drm: omapdrm: tiler: Fix module autoload for OF platform driver

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Message-ID: <20150924153620.GA28419@goodgumbo.baconseed.org>
Date:	Thu, 24 Sep 2015 17:36:20 +0200
From:	Luis de Bethencourt <luis@...ethencourt.com>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Grygorii Strashko <grygorii.strashko@...aro.org>,
	Rob Clark <robdclark@...il.com>,
	dri-devel@...ts.freedesktop.org,
	Javier Martinez Canillas <javier@....samsung.com>
Subject: Re: [PATCH 3/5] drm: omapdrm: tiler: Fix module autoload for OF
 platform driver

On Thu, Sep 24, 2015 at 01:41:56PM +0300, Tomi Valkeinen wrote:
> 
> On 17/09/15 17:21, Luis de Bethencourt wrote:
> > This platform driver has a OF device ID table but the OF module
> > alias information is not created so module autoloading won't work.
> > 
> > Signed-off-by: Luis de Bethencourt <luisbg@....samsung.com>
> > ---
> >  drivers/gpu/drm/omapdrm/omap_dmm_tiler.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
> > index 7841970..ecbc9e5 100644
> > --- a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
> > +++ b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
> > @@ -1014,6 +1014,7 @@ static const struct of_device_id dmm_of_match[] = {
> >  	},
> >  	{},
> >  };
> > +MODULE_DEVICE_TABLE(of, dmm_of_match);
> >  #endif
> >  
> >  struct platform_driver omap_dmm_driver = {
> 
> I think this one is not needed.
> 
> Tiler cannot be compiled as a module. Or, to be more exact, the tiler
> driver is included in the omapdrm module, along with the main omapdrm
> driver, which can be a module.
> 
> The autoloading should happen via omapdrm, and when that happens, tiler
> driver comes along.
> 
>  Tomi
> 

Hi Tomi,

I am a bit confused.

So how the OMAP DRM auto loading is supposed to work when using Device Trees?
As far as I can tell, the main omap drm driver does not have a OF device ID
table and a .of_match it only has a MODULE_ALIAS("platform:" DRIVER_NAME),
but the tiler driver (that is built-in the omap drm driver) does have a a
OF device ID table and I see in DTS that are device nodes using those compatible
strings

$ git grep omap4-dmm arch/arm/boot/dts/omap*
arch/arm/boot/dts/omap4.dtsi:                   compatible = "ti,omap4-dmm";

Does that mean there is no need for MODULE_ALIAS("platform:" DMM_DRIVER_NAME)?

Because right now omapdrm.ko is exporting the alias for legacy / platform
device registration but not for OF.

Thanks,
Luis
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