Re: [PATCH 6/9] drm/xen-front: Introduce DRM/KMS virtual display driver

[Oleksandr Andrushchenko]

On 02/23/2018 05:12 PM, Boris Ostrovsky wrote:
> On 02/21/2018 03:03 AM, Oleksandr Andrushchenko wrote:
>
> > +
> > +struct drm_driver xen_drm_driver = {
> > +	.driver_features           = DRIVER_GEM | DRIVER_MODESET |
> > +				     DRIVER_PRIME | DRIVER_ATOMIC,
> > +	.lastclose                 = lastclose,
> > +	.gem_free_object_unlocked  = free_object,
> > +	.gem_vm_ops                = &xen_drm_vm_ops,
> > +	.prime_handle_to_fd        = drm_gem_prime_handle_to_fd,
> > +	.prime_fd_to_handle        = drm_gem_prime_fd_to_handle,
> > +	.gem_prime_import          = drm_gem_prime_import,
> > +	.gem_prime_export          = drm_gem_prime_export,
> > +	.gem_prime_get_sg_table    = prime_get_sg_table,
> > +	.gem_prime_import_sg_table = prime_import_sg_table,
> > +	.gem_prime_vmap            = prime_vmap,
> > +	.gem_prime_vunmap          = prime_vunmap,
> > +	.gem_prime_mmap            = prime_mmap,
> > +	.dumb_create               = dumb_create,
> > +	.fops                      = &xendrm_fops,
> > +	.name                      = "xendrm-du",
> > +	.desc                      = "Xen PV DRM Display Unit",
> > +	.date                      = "20161109",
> You must have been working on this for a while ;-)
yes, this is true ;)
> I assume this needs to be updated.
It can be, but I would either stick to the current value
for historical reasons or would update it in the final version
of the driver, so it reflects the date of issuing ;)
> > +bool xen_drm_front_drv_is_used(struct platform_device *pdev)
> > +{
> > +	struct xen_drm_front_drm_info *drm_info = platform_get_drvdata(pdev);
> > +	struct drm_device *dev;
> > +
> > +	if (!drm_info)
> > +		return false;
> > +
> > +	dev = drm_info->drm_dev;
> > +	if (!dev)
> > +		return false;
> > +
> > +	/*
> > +	 * FIXME: the code below must be protected by drm_global_mutex,
> > +	 * but it is not accessible to us. Anyways there is a race condition,
> > +	 * but we will re-try.
> > +	 */
> > +	return dev->open_count != 0;
> Would it be a problem, given the race, if you report that the frontend
> is not in use, while it actually is?
no, backend will not be able to activate us again
> -boris