[PATCH] drm/vkms: Add support for vkms work without vblank

[Daniel Vetter]

On Mon, Aug 20, 2018 at 08:55:44PM -0300, Rodrigo Siqueira wrote:
> Currently, vkms needs VBlank to work well. This patch adds another
> operation model that make vkms works without VBlank support.
> 
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo at gmail.com>
> ---
>  drivers/gpu/drm/vkms/vkms_crtc.c | 10 ++++++++++
>  drivers/gpu/drm/vkms/vkms_drv.c  | 12 ++++++++++--
>  drivers/gpu/drm/vkms/vkms_drv.h  |  1 +
>  3 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index bfe6e0312cc4..001fa5c1d326 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -145,12 +145,22 @@ static const struct drm_crtc_funcs vkms_crtc_funcs = {
>  static void vkms_crtc_atomic_enable(struct drm_crtc *crtc,
>  				    struct drm_crtc_state *old_state)
>  {
> +	struct vkms_output *vkms_out = drm_crtc_to_vkms_output(crtc);
> +
> +	if (vkms_out->disable_vblank)
> +		return;
> +
>  	drm_crtc_vblank_on(crtc);
>  }
>  
>  static void vkms_crtc_atomic_disable(struct drm_crtc *crtc,
>  				     struct drm_crtc_state *old_state)
>  {
> +	struct vkms_output *vkms_out = drm_crtc_to_vkms_output(crtc);
> +
> +	if (vkms_out->disable_vblank)
> +		return;
> +
>  	drm_crtc_vblank_off(crtc);
>  }
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index 5d78bd97e69c..f30c4113d4c4 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -21,6 +21,10 @@
>  
>  static struct vkms_device *vkms_device;
>  
> +static bool disable_vblank;
> +module_param_named(disablevblank, disable_vblank, bool, 0444);
> +MODULE_PARM_DESC(disablevblank, "Disable vblank interrupt");

I think the info output is much clearer, I'd rename this to virtual_hw,
with 0 as default, and a help text along of "Enable virtual HW mode
(disables vblanks and immediately completes flips)."

> +
>  static const struct file_operations vkms_driver_fops = {
>  	.owner		= THIS_MODULE,
>  	.open		= drm_open,
> @@ -105,9 +109,13 @@ static int __init vkms_init(void)
>  		goto out_fini;
>  	}
>  
> -	vkms_device->drm.irq_enabled = true;
> +	vkms_device->output.disable_vblank = disable_vblank;
> +	vkms_device->drm.irq_enabled = !disable_vblank ? true : false;
> +
> +	if (disable_vblank)
> +		DRM_INFO("Virtual Hardware mode enabled");
>  
> -	ret = drm_vblank_init(&vkms_device->drm, 1);
> +	ret = (disable_vblank) ? 0 : drm_vblank_init(&vkms_device->drm, 1);
>  	if (ret) {
>  		DRM_ERROR("Failed to vblank\n");
>  		goto out_fini;
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index f156c930366a..9ee862e6f7e5 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -52,6 +52,7 @@ struct vkms_output {
>  	struct drm_encoder encoder;
>  	struct drm_connector connector;
>  	struct hrtimer vblank_hrtimer;
> +	bool disable_vblank;
>  	ktime_t period_ns;
>  	struct drm_pending_vblank_event *event;
>  	bool crc_enabled;

The vblank handling parts look correct to me.

Does kms_flip work with this? Virtual hw immediately completes the
drm_crtc_state->event in the atomic_update callback, that part seems to be
missing from your patch.

Also I like the idea of switching away from the generic -EINVAL to -ENOTTY
for when vblanks aren't supported. Do you have that somewhere (as a
separate patch).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch