Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Ville Syrjälä]

On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> From: Stefan Christ <s.christ@xxxxxxxxx>
> 
> Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> based OpenGL(ES)/EGL implementations may require the ioctl to
> synchronize drawing or buffer flip for double buffering. It is tested on
> the i.MX6.
> 
> Code is based on
>     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> 
> Signed-off-by: Stefan Christ <s.christ@xxxxxxxxx>
> Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
>  include/drm/drm_fb_helper.h     |  5 ++-
>  2 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index e934b541feea..39a3532e311c 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>  EXPORT_SYMBOL(drm_fb_helper_setcmap);
>  
>  /**
> + * drm_fb_helper_ioctl - legacy ioctl implementation
> + * @info: fbdev registered by the helper
> + * @cmd: ioctl command
> + * @arg: ioctl argument
> + *
> + * A helper to implement the standard fbdev ioctl. Only
> + * FBIO_WAITFORVSYNC is implemented for now.
> + */
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +	unsigned int i;
> +	int ret = 0;
> +
> +	drm_modeset_lock_all(dev);
> +	if (!drm_fb_helper_is_bound(fb_helper)) {
> +		drm_modeset_unlock_all(dev);
> +		return -EBUSY;
> +	}
> +
> +	switch (cmd) {
> +	case FBIO_WAITFORVSYNC:
> +		for (i = 0; i < fb_helper->crtc_count; i++) {

FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
to do this for all the crtcs. Though what that crtc means for fb is
rather poorly defined.

> +			struct drm_mode_set *mode_set;
> +			struct drm_crtc *crtc;
> +
> +			mode_set = &fb_helper->crtc_info[i].mode_set;
> +			crtc = mode_set->crtc;
> +
> +			/*
> +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> +			 * are currently enabled.
> +			 */
> +			if (!crtc->enabled)
> +				continue;
> +
> +			ret = drm_crtc_vblank_get(crtc);
> +			if (!ret) {
> +				drm_crtc_wait_one_vblank(crtc);
> +				drm_crtc_vblank_put(crtc);
> +			}

This looks quite sub-optimal. It should rather do something along the
lines of what drm_atomic_helper_wait_for_vblanks() does.

> +		}
> +		goto unlock;
> +	default:
> +		ret = -ENOTTY;
> +	}
> +
> +unlock:
> +	drm_modeset_unlock_all(dev);
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_ioctl);
> +
> +/**
>   * drm_fb_helper_check_var - implementation for ->fb_check_var
>   * @var: screeninfo to check
>   * @info: fbdev registered by the helper
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 975deedd593e..460be9d9fa98 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -230,7 +230,8 @@ struct drm_fb_helper {
>  	.fb_blank	= drm_fb_helper_blank, \
>  	.fb_pan_display	= drm_fb_helper_pan_display, \
>  	.fb_debug_enter = drm_fb_helper_debug_enter, \
> -	.fb_debug_leave = drm_fb_helper_debug_leave
> +	.fb_debug_leave = drm_fb_helper_debug_leave, \
> +	.fb_ioctl	= drm_fb_helper_ioctl
>  
>  #ifdef CONFIG_DRM_FBDEV_EMULATION
>  void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> @@ -286,6 +287,8 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
>  
>  int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
>  
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg);
> +
>  int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
>  int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
>  int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
> -- 
> git-series 0.8.11
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-- 
Ville Syrjälä
Intel OTC