linux-kernel - Re: [PATCH v4 9/9] drm/vkms: convert to use faux

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Message-ID: <Z9MT23hgX2c21xNA@fedora>
Date: Thu, 13 Mar 2025 18:20:27 +0100
From: José Expósito <jose.exposito89@...il.com>
To: Simona Vetter <simona.vetter@...ll.ch>
Cc: Greg KH <gregkh@...uxfoundation.org>, Jonathan.Cameron@...wei.com,
	airlied@...il.com, aleksander.lobakin@...el.com,
	andriy.shevchenko@...ux.intel.com, bhelgaas@...gle.com,
	broonie@...nel.org, dakr@...nel.org,
	dri-devel@...ts.freedesktop.org, hamohammed.sa@...il.com,
	lgirdwood@...il.com, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, louis.chauvet@...tlin.com,
	lukas@...ner.de, lyude@...hat.com,
	maarten.lankhorst@...ux.intel.com, mairacanal@...eup.net,
	melissa.srw@...il.com, mripard@...nel.org, quic_zijuhu@...cinc.com,
	rafael@...nel.org, robin.murphy@....com,
	rust-for-linux@...r.kernel.org, simona@...ll.ch,
	tzimmermann@...e.de
Subject: Re: [PATCH v4 9/9] drm/vkms: convert to use faux_device

On Thu, Mar 13, 2025 at 03:22:21PM +0100, Simona Vetter wrote:
> On Wed, Mar 12, 2025 at 07:22:07AM +0100, Greg KH wrote:
> > On Tue, Mar 11, 2025 at 06:20:53PM +0100, José Expósito wrote:
> > > Hi everyone,
> > > 
> > > > On Tue, Feb 25, 2025 at 02:51:40PM +0100, Louis Chauvet wrote:
> > > > > 
> > > > > 
> > > > > Le 25/02/2025 à 12:41, Thomas Zimmermann a écrit :
> > > > > > Hi
> > > > > > 
> > > > > > Am 10.02.25 um 15:37 schrieb Louis Chauvet:
> > > > > > > On 10/02/25 - 13:30, Greg Kroah-Hartman wrote:
> > > > > > > > The vkms driver does not need to create a platform device, as there is
> > > > > > > > no real platform resources associated it,  it only did so because it was
> > > > > > > > simple to do that in order to get a device to use for resource
> > > > > > > > management of drm resources.  Change the driver to use the faux device
> > > > > > > > instead as this is NOT a real platform device.
> > > > > > > > 
> > > > > > > > Cc: Louis Chauvet <louis.chauvet@...tlin.com>
> > > > > > > > Cc: Haneen Mohammed <hamohammed.sa@...il.com>
> > > > > > > > Cc: Simona Vetter <simona@...ll.ch>
> > > > > > > > Cc: Melissa Wen <melissa.srw@...il.com>
> > > > > > > > Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> > > > > > > > Cc: Maxime Ripard <mripard@...nel.org>
> > > > > > > > Cc: Thomas Zimmermann <tzimmermann@...e.de>
> > > > > > > > Cc: David Airlie <airlied@...il.com>
> > > > > > > > Cc: dri-devel@...ts.freedesktop.org
> > > > > > > > Reviewed-by: Lyude Paul <lyude@...hat.com>
> > > > > > > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > > > > 
> > > > > > Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
> > > > > > 
> > > > > > > Tested-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > > > > > > Reviewed-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > > > > > > 
> > > > > > > Thanks for the modification, it seems to work.
> > > > > > 
> > > > > > Should this patch be merged through DRM trees? drm-misc-next is at
> > > > > > v6.14-rc4 and has struct faux_device.
> > > > > 
> > > > > Hi,
> > > > > 
> > > > > I was not aware the faux-device was merged, as it is a new feature, I
> > > > > expected it to reach drm-misc-next on 6.15-rc1.
> > > > 
> > > > I added it to Linus's tree just so that DRM could get these changes into
> > > > their tree now :)
> > > > 
> > > > > I plan to merge [1] today/tomorrow (well tested with platform_device), and
> > > > > then I will submit an updated version of this patch (only trivial conflicts,
> > > > > but never tested with multiple VKMS devices).
> > > > > 
> > > > > [1]:https://lore.kernel.org/all/20250218101214.5790-1-jose.exposito89@gmail.com/
> > > > 
> > > > Great, thanks!
> > > > 
> > > > greg k-h
> > > 
> > > Testing this patch again as part of some IGT tests I'm working on,
> > > I noticed that, applying this patch on top of the latest drm-misc-next
> > > triggers a warning at drivers/gpu/drm/drm_gem.c:571, in
> > > drm_gem_get_pages():
> > > 
> > >     if (WARN_ON(!obj->filp))
> > >             return ERR_PTR(-EINVAL);
> > 
> > I don't see how the faux bus change would have anything to do with a
> > filp as that's not related as far as I can tell.  But I don't know the
> > drm layer at all, where does that filp come from?
> 
> Yeah that filp is the shmem file that backs gem bo. That's very far away
> from anything device/driver related datastrctures. If this is a new
> failure due to the aux bux conversion then it would be really surprising.

Agreed, I find it surprising, but reverting the patch removes the warning.

It's most likely an issue on my side, but I decided to double check just
in case someone else is also seeing this warning.

Jose

> -Sima
> 
> -- 
> Simona Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch