Re: [PATCH] drm/i915: Fix IPS related flicker

Kenneth Graunke
2015-05-28T23:57:52Z

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On Thursday, May 21, 2015 12:53:03 PM Rodrigo Vivi wrote:
> We cannot let IPS enabled with no plane on the pipe:
>
> BSpec: "IPS cannot be enabled until after at least one plane has
> been enabled for at least one vertical blank." and "IPS must be
> disabled while there is still at least one plane enabled on the
> same pipe as IPS.
>
> However this shortcut path to make primary plane invisible when
> updating primary plane was leting IPS enabled while there was no
> other plane enabled on the pipe causing flickerings that we were
> believing that it was caused by that other restriction where
> ips cannot be used when pixel rate is greater than 95% of cdclok.
>
> Reference: https://bugs.freedesktop.org/show_bug.cgi?id=85583
> Cc: Joe Konno <joe.konno@intel.com>
> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
> drivers/gpu/drm/i915/intel_display.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 9d2d6fb..5519d56 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -2789,6 +2789,19 @@ static void ironlake_update_primary_plane(struct drm_crtc *crtc,
> int pixel_size;
>
> if (!visible || !fb) {
> + /*
> + * This shortcut path disables the primary plane making
> + * IPS really sad and lost when it is enabled alone with no
> + * plane around on the pipe. So, for now it is safe to disable
> + * IPS here.
> + /
> + /*
> + * FIXME: Any other plane enabled should be enough so it would
> + * be better to check if there is really no sprite or
> + * cursor around.
> + */
> + hsw_disable_ips(intel_crtc);
> +
> I915_WRITE(reg, 0);
> I915_WRITE(DSPSURF(plane), 0);
> POSTING_READ(reg);

This fixes a bug on my Lenovo X250 (Broadwell GT2).

1. Boot
2. startx using SNA and KDE 5
3. Quit X

Prior to this patch, the screen was all scrambled. With this patch, it
works perfectly.

Thanks, Rodrigo!

Tested-by: Kenneth Graunke <kenneth@whitecape.org>

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