linux-kernel - Re: [PATCHv3 2/3] drm/prime: Introduce drm_gem_prime_import

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Message-ID: <20170503152439.GH8277@nuc-i3427.alporthouse.com>
Date:   Wed, 3 May 2017 16:24:39 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Laura Abbott <labbott@...hat.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Sumit Semwal <sumit.semwal@...aro.org>,
        intel-gfx@...ts.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
Subject: Re: [PATCHv3 2/3] drm/prime: Introduce drm_gem_prime_import_platform

On Wed, May 03, 2017 at 05:07:03PM +0200, Daniel Vetter wrote:
> On Wed, May 03, 2017 at 07:40:51AM -0700, Laura Abbott wrote:
> > On 05/03/2017 12:39 AM, Daniel Vetter wrote:
> > > On Tue, May 02, 2017 at 09:22:13PM +0100, Chris Wilson wrote:
> > >> On Tue, May 02, 2017 at 10:02:07AM -0700, Laura Abbott wrote:
> > >>>  /**
> > >>> + * drm_gem_prime_import_platform - alternate implementation of the import callback
> > >>> + * @dev: drm_device to import into
> > >>> + * @dma_buf: dma-buf object to import
> > >>> + *
> > >>> + * This is identical to drm_gem_prime_import except the device used for dma_buf
> > >>> + * attachment is an internal platform device instead of the standard device
> > >>> + * structure. The use of this function should be limited to drivers that do not
> > >>> + * set up an underlying device structure.
> > >>> + */
> > >>> +struct drm_gem_object *drm_gem_prime_import_platform(struct drm_device *dev,
> > >>
> > >> Simpler soluation will be for the caller to provide the platformdev?
> > >>
> > >> That works nicely for the vgem case, I think.
> > > 
> > > Yeah looking at this again, do we really need this patch? Couldn't we
> > > instead change patch 1 to first allocate the fake platform device, then
> > > pass that to drm_dev_alloc (instead of NULL like we do now)?
> > > 
> > 
> > That was what I proposed in the first version and it was rejected.
> > It's useful to have at least one driver with a NULL device for testing
> > edge cases.
> 
> Oh drat :( I'd say dropping the coverage for NULL testing is ok, there's
> no other driver than vgem using this. And now that we have vgem dma-buf
> (or will, soonish) I'd expect that the same will hold for vkms, if it ever
> happens.

This series creates vgem->platformdev which we can just pass to
drm_gem_prime_import_platform() (or equivalent drm_gem_prime function that
takes an explicit dev). It was a bit of a surprise that import_platform
didn't take the platformdev after going to the trouble of creating
vgem->platformdev.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre