[Intel-gfx] [PATCH v2 9/5] drm/i915: Draw a picture about video timings

[Imre Deak]

On Thu, 2014-02-20 at 13:14 +0200, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> The docs are a bit lacking when it comes to describing when certain
> timing related events occur in the hardware. Draw a picture which
> tries to capture the most important ones.
> 
> v2: Clarify a few details (Imre)
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 49 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 40adce0..ed0df3e 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -625,6 +625,55 @@ i915_pipe_enabled(struct drm_device *dev, int pipe)
>  	}
>  }
>  
> +/*
> + * This timing diagram depicts the video signal in and
> + * around the vertical blanking period.
> + *
> + * Assumptions about the fictitious mode used in this example:
> + *  vblank_start >= 3
> + *  vsync_start = vblank_start + 1
> + *  vsync_end = vblank_start + 2
> + *  vtotal = vblank_start + 3
> + *
> + *           start of vblank:
> + *           latch double buffered registers
> + *           increment frame counter (ctg+)
> + *           generate start of vblank interrupt (gen4+)
> + *           |
> + *           |          frame start:
> + *           |          generate frame start interrupt (aka. vblank interrupt) (gmch)
> + *           |          may be shifted forward 1-3 extra lines via PIPECONF
> + *           |          |
> + *           |          |  start of vsync:
> + *           |          |  generate vsync interrupt
> + *           |          |  |
> + * ___xxxx___    ___xxxx___    ___xxxx___    ___xxxx___    ___xxxx___    ___
> + *       .   \hs/   .      \hs/          \hs/          \hs/   .      \hs/
> + * ----va---> <-----------------vb--------------------> <--------va---------
> + *       |          |       <----vs----->                     |
> + * -vbs-----> <---vbs+1---> <---vbs+2---> <-----0-----> <-----1-----> <---2- (scanline counter gen2)
> + * -vbs-2---> <---vbs-1---> <---vbs-----> <---vbs+1---> <---vbs+2---> <---0- (scanline counter gen3+)
> + *       |          |                                         |
> + *       last visible pixel                                   first visible pixel
> + *                  |                                         increment frame counter (gen3/4)
> + *                  pixel counter = vblank_start * htotal     pixel counter = 0 (gen3/4)
> + *
> + * x  = horizontal active
> + * _  = horizontal blanking
> + * hs = horizontal sync
> + * va = vertical active
> + * vb = vertical blanking
> + * vs = vertical sync
> + * vbs = vblank_start (number)
> + *
> + * Summary:
> + * - most events happen at the start of horizontal sync
> + * - frame start happens at the start of horizontal blank, 1-4 lines
> + *   (depending on PIPECONF settings) after the start of vblank
> + * - gen3/4 pixel and frame counter are synchronized with the start
> + *   of horizontal active on the first line of vertical active

A nice description that I haven't found in any docs, so:
Acked-by: Imre Deak <imre.deak at intel.com>

> + */
> +
>  static u32 i8xx_get_vblank_counter(struct drm_device *dev, int pipe)
>  {
>  	/* Gen2 doesn't have a hardware frame counter */

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