Nice illustration of the various events in a Video signal.
Reviewed-by: "Akash Goel <akash.go...@gmail.com>"
On Tue, Apr 29, 2014 at 4:05 PM, <ville.syrj...@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrj...@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)
>
> Acked-by: Imre Deak <imre.d...@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrj...@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 742f276..bc4585b 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -669,6 +669,55 @@ 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
> + */
> +
> static u32 i8xx_get_vblank_counter(struct drm_device *dev, int pipe)
> {
> /* Gen2 doesn't have a hardware frame counter */
> --
> 1.8.3.2
>
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