linux-kernel - Re: [PATCH] drm/virtio: implement virtio_gpu

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Message-ID: <20250518175332-mutt-send-email-mst@kernel.org>
Date: Sun, 18 May 2025 17:53:59 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Gerd Hoffmann <kraxel@...hat.com>
Cc: Maxime Ripard <mripard@...nel.org>, dri-devel@...ts.freedesktop.org,
	Eric Auger <eric.auger@...hat.com>,
	David Airlie <airlied@...hat.com>,
	Gurchetan Singh <gurchetansingh@...omium.org>,
	Chia-I Wu <olvaffe@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Simona Vetter <simona@...ll.ch>,
	"open list:VIRTIO GPU DRIVER" <virtualization@...ts.linux.dev>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/virtio: implement virtio_gpu_shutdown

On Tue, May 13, 2025 at 12:18:44PM +0200, Gerd Hoffmann wrote:
> > > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
> > > index e32e680c7197..71c6ccad4b99 100644
> > > --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
> > > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
> > > @@ -130,10 +130,10 @@ static void virtio_gpu_remove(struct virtio_device *vdev)
> > >  
> > >  static void virtio_gpu_shutdown(struct virtio_device *vdev)
> > >  {
> > > -	/*
> > > -	 * drm does its own synchronization on shutdown.
> > > -	 * Do nothing here, opt out of device reset.
> > > -	 */
> > > +	struct drm_device *dev = vdev->priv;
> > > +
> > > +	/* stop talking to the device */
> > > +	drm_dev_unplug(dev);
> > 
> > I'm not necessarily opposed to using drm_dev_unplug() here, but it's
> > still pretty surprising to me. It's typically used in remove, not
> > shutdown. The typical helper to use at shutdown is
> > drm_atomic_helper_shutdown.
> > 
> > So if the latter isn't enough or wrong, we should at least document why.
> 
> The intention of this is to make sure the driver stops talking to the
> device (as the comment already says).
> 
> There are checks in place in the virt queue functions which will make
> sure the driver will not try place new requests in the queues after
> drm_dev_unplug() has been called.  Which why I decided to implement it
> that way.
> 
> drm_atomic_helper_shutdown() tears down all outputs according to the
> documentation.  Which is something different.  I don't think calling
> drm_atomic_helper_shutdown() will do what I need here.  Calling it in
> addition to drm_dev_unplug() might make sense, not sure.
> 
> Suggestions are welcome.
> 
> take care,
>   Gerd


I suggest adding comments in code explaining why it's approriate here.
Want to try?

-- 
MST