Re: [PATCH v2 1/8] drm: Disable the cursor plane on atomic contexts with virtualized drivers

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Daniel Vetter <daniel@xxxxxxxx> writes:

> On Mon, Jul 11, 2022 at 11:32:39PM -0400, Zack Rusin wrote:
>> From: Zack Rusin <zackr@xxxxxxxxxx>
>> Cursor planes on virtualized drivers have special meaning and require
>> that the clients handle them in specific ways, e.g. the cursor plane
>> should react to the mouse movement the way a mouse cursor would be
>> expected to and the client is required to set hotspot properties on it
>> in order for the mouse events to be routed correctly.
>> This breaks the contract as specified by the "universal planes". Fix it
>> by disabling the cursor planes on virtualized drivers while adding
>> a foundation on top of which it's possible to special case mouse cursor
>> planes for clients that want it.
>> Disabling the cursor planes makes some kms compositors which were broken,
>> e.g. Weston, fallback to software cursor which works fine or at least
>> better than currently while having no effect on others, e.g. gnome-shell
>> or kwin, which put virtualized drivers on a deny-list when running in
>> atomic context to make them fallback to legacy kms and avoid this issue.
>> Signed-off-by: Zack Rusin <zackr@xxxxxxxxxx>
>> Fixes: 681e7ec73044 ("drm: Allow userspace to ask for universal plane list (v2)")


>> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
>> index f6159acb8856..c4cd7fc350d9 100644
>> --- a/include/drm/drm_drv.h
>> +++ b/include/drm/drm_drv.h
>> @@ -94,6 +94,16 @@ enum drm_driver_feature {
>>  	 * synchronization of command submission.
>>  	 */
>> +	/**
>> +	 *
>> +	 * Driver is running on top of virtual hardware. The most significant
>> +	 * implication of this is a requirement of special handling of the
>> +	 * cursor plane (e.g. cursor plane has to actually track the mouse
>> +	 * cursor and the clients are required to set hotspot in order for
>> +	 * the cursor planes to work correctly).
>> +	 */
>> +	DRIVER_VIRTUAL                  = BIT(7),
> I think the naming here is unfortunate, because people will vonder why
> e.g. vkms doesn't set this, and then add it, and confuse stuff completely.
> Also it feels a bit wrong to put this onto the driver, when really it's a
> cursor flag. I guess you can make it some kind of flag in the drm_plane
> structure, or a new plane type, but putting it there instead of into the
> "random pile of midlayer-mistake driver flags" would be a lot better.
> Otherwise I think the series looks roughly how I'd expect it to look.
> -Daniel

AFAICT this is the only remaining thing to be addressed for this series ?

Zack, are you planning to re-spin a v3 of this patch-set? Asking because
we want to take virtio-gpu out of the atomic KMS deny list in mutter, but
first need this to land.

If you think that won't be able to do it in the short term, Bilal (Cc'ed)
or me would be glad to help with that.

Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

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