Re: [PATCH] drm/i915/chv: Remove DPIO force latency causing interpair skew issue

Ville Syrjälä
2015-04-09T20:20:49Z

On Thu, Apr 09, 2015 at 10:17:05AM -0700, clinton.a.taylor@intel.com wrote:
> From: Clint Taylor <clinton.a.taylor@intel.com>
>
> Latest version of the "CHV DPIO programming notes" no longer requires writes
> to TX DW 11 to fix a +2UI interpair skew issue. The current code from
> April 2014 was actually causing additional skew issues between all
> TMDS pairs.
>
> Signed-off-by: Clint Taylor <clinton.a.taylor@intel.com>
> ---
> drivers/gpu/drm/i915/intel_hdmi.c | 5 -----
> 1 file changed, 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
> index 26222e6..3cef326 100644
> --- a/drivers/gpu/drm/i915/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/intel_hdmi.c
> @@ -1515,11 +1515,6 @@ static void chv_hdmi_pre_enable(struct intel_encoder *encoder)
>
> /* Program Tx latency optimal setting */
> for (i = 0; i < 4; i++) {
> - /* Set the latency optimal bit */
> - data = (i == 1) ? 0x0 : 0x6;
> - vlv_dpio_write(dev_priv, pipe, CHV_TX_DW11(ch, i),
> - data << DPIO_FRC_LATENCY_SHFIT);
> -

On a huch I went and tried this same treatment on intel_dp.c and it
fixes the remaining link training issues [1] I've been seeing \o/
I still need to try with the other DP display that was having these
problems, but that'll have to wait until tomorrow.

So please respin this with the same change made to intel_dp.c (someone
should really eliminate the code duplication we have going on there), and
assuming my test with the other display goes as well I can then post
some DPIO lane power gating patches which I've been holding back because
they made the problem worse.

[1] http://lists.freedesktop.org/archives/intel-gfx/2015-February/059877.html

> /* Set the upar bit */
> data = (i == 1) ? 0x0 : 0x1;
> vlv_dpio_write(dev_priv, pipe, CHV_TX_DW14(ch, i),
> --
> 1.7.9.5
>
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--
Ville Syrjälä
Intel OTC