linux-kernel - Re: [PATCH v5] drm/virtio: Add option to disable KMS support

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Date:   Thu, 2 Mar 2023 08:25:31 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     Rob Clark <robdclark@...il.com>, dri-devel@...ts.freedesktop.org,
        Chia-I Wu <olvaffe@...il.com>,
        Ryan Neph <ryanneph@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Clark <robdclark@...omium.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        David Airlie <airlied@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] drm/virtio: Add option to disable KMS support

On Thu, Mar 02, 2023 at 12:39:33AM +0300, Dmitry Osipenko wrote:
> On 3/1/23 21:54, Rob Clark wrote:
> >  /* virtgpu_display.c */
> > +#if defined(CONFIG_DRM_VIRTIO_GPU_KMS)
> >  int virtio_gpu_modeset_init(struct virtio_gpu_device *vgdev);
> >  void virtio_gpu_modeset_fini(struct virtio_gpu_device *vgdev);
> > +#else
> > +static inline int virtio_gpu_modeset_init(struct virtio_gpu_device *vgdev)
> > +{
> > +	return 0;
> > +}
> > +static inline void virtio_gpu_modeset_fini(struct virtio_gpu_device *vgdev)
> > +{
> > +}
> > +#endif
> 
> In v4 Gerd wanted to keep building the virtgpu_display.o and instead add
> the KSM config check to virtio_gpu_modeset_init/fini().

The main point is that the code workflow should be the same in both
cases.  The patch does that for virtio_gpu_modeset_init() but doesn't
for virtio_gpu_modeset_fini().

Return early in the functions (and drop the #ifdef here) is how I would
implement this, but I wouldn't insist on that, there are other ways to
solve this too ;)

take care,
  Gerd