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

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Date:	Thu, 24 Sep 2015 18:06:16 +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 06:43:33PM +0300, Tomi Valkeinen wrote:
> 
> On 24/09/15 18:36, Luis de Bethencourt wrote:
> 
> > I am a bit confused.
> 
> Yes, it's an interesting mess due to legacy reasons. Maybe we manage to
> fix it some day...
> 
> > So how the OMAP DRM auto loading is supposed to work when using Device Trees?
> 
> omapdrm isn't a real HW device driver at the moment. There's another
> driver, omapdss, which is the HW driver, and omapdrm uses omapdss.
> omapdrm platform device is created by omap platform code at boot time,
> the same way for both DT and non-DT boots.
> 
> > 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)?
> 
> No, I think that's the thing that makes omapdrm load.
> 
>  Tomi
> 

Makes sense. Thank you for the explanation.

I didn't know that a omapdrm platform device was registered explictly by platform
code.

Please notice that I wrote MODULE_ALIAS("platform:" DMM_DRIVER_NAME) not
MODULE_ALIAS("platform:" DRIVER_NAME)
In other words, I meant if alias: platform:dmm is needed besides alias:
platform:omapdrm?

Thanks,
Luis
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