Re: [PATCH 7/7] drm/i915: wait for actual vblank, not just 20ms

[Owain Ainsworth <zerooa@googlemail.com>]

On Wed, Aug 18, 2010 at 12:00:36PM -0700, Jesse Barnes wrote:
> Waiting for a hard coded 20ms isn't always enough to make sure a vblank
> period has actually occurred, so add code to make sure we really have
> passed through a vblank period (or that the pipe is off when disabling).
> 
> This prevents problems with mode setting and link training, and seems to
> fix a bug like https://bugs.freedesktop.org/show_bug.cgi?id=29278, but
> on an HP 8440p instead.  Hopefully also fixes
> https://bugs.freedesktop.org/show_bug.cgi?id=29141.
> 
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/i915_reg.h      |    1 +
>  drivers/gpu/drm/i915/intel_crt.c     |    2 +-
>  drivers/gpu/drm/i915/intel_display.c |   75 ++++++++++++++++++++++++++--------
>  drivers/gpu/drm/i915/intel_dp.c      |    3 +-
>  drivers/gpu/drm/i915/intel_drv.h     |    3 +-
>  drivers/gpu/drm/i915/intel_sdvo.c    |    3 +-
>  drivers/gpu/drm/i915/intel_tv.c      |    9 ++--
>  7 files changed, 71 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index cf41c67..822b21c 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -2080,6 +2080,7 @@
>  #define PIPE_DITHER_TYPE_ST01		(1 << 2)
>  /* Pipe A */
>  #define PIPEADSL		0x70000
> +#define   DSL_LINEMASK	       	0x00000fff
>  #define PIPEACONF		0x70008
>  #define   PIPEACONF_ENABLE	(1<<31)
>  #define   PIPEACONF_DISABLE	0
> diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
> index ee0732b..4a2f593 100644
> --- a/drivers/gpu/drm/i915/intel_crt.c
> +++ b/drivers/gpu/drm/i915/intel_crt.c
> @@ -331,7 +331,7 @@ intel_crt_load_detect(struct drm_crtc *crtc, struct intel_encoder *intel_encoder
>  		I915_WRITE(pipeconf_reg, pipeconf | PIPECONF_FORCE_BORDER);
>  		/* Wait for next Vblank to substitue
>  		 * border color for Color info */
> -		intel_wait_for_vblank(dev);
> +		intel_wait_for_vblank(dev, pipe);
>  		st00 = I915_READ8(VGA_MSR_WRITE);
>  		status = ((st00 & (1 << 4)) != 0) ?
>  			connector_status_connected :
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 928bcc2..27e60b8 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -972,11 +972,57 @@ intel_find_pll_g4x_dp(const intel_limit_t *limit, struct drm_crtc *crtc,
>      return true;
>  }
>  
> -void
> -intel_wait_for_vblank(struct drm_device *dev)
> +/**
> + * intel_wait_for_vblank - wait for vblank on a given pipe
> + * @dev: drm device
> + * @pipe: pipe to wait for
> + *
> + * Wait for vblank to occur on a given pipe.  Needed for various bits of
> + * mode setting code.
> + */
> +void intel_wait_for_vblank(struct drm_device *dev, int pipe)
> +{
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	int pipestat_reg = (pipe == 0 ? PIPEASTAT : PIPEBSTAT);
> +	unsigned long timeout = jiffies + msecs_to_jiffies(100);
> +
> +	/* Wait for vblank interrupt bit to set */
> +	while (!(I915_READ(pipestat_reg) & PIPE_VBLANK_INTERRUPT_STATUS) &&
> +	       time_after(timeout, jiffies))
> +		mdelay(1);

Why not actually go to sleep and let the interrupt wake you up? let the
machine do something else in the meantime.

-0-
-- 
You cannot kill time without injuring eternity.