linux-kernel - Re: [Intel-gfx] [PATCH 5/7] drm/i915: Make DP prepare/commit consistent with DP dpms

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Date:	Thu, 03 Nov 2011 15:30:57 -0700
From:	Keith Packard <keithp@...thp.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 5/7] drm/i915: Make DP prepare/commit consistent with DP dpms

On Thu, 3 Nov 2011 13:00:11 -0700, Jesse Barnes <jbarnes@...tuousgeek.org> wrote:

> A few comments on this one (also, is it strictly required to fix your
> bug)?

I think so; the panel definitely was not happy when I turned the link
off while the panel power was on. Having the mode setting and DPMS paths
doing things in different orders definitely doesn't seem reasonable
though. I nearly managed to share code between the two paths, but there
are subtle differences in requirements and so I didn't bother.

> Ok so you're making sure the panel has power to down the link, I think
> that's fine.

No, I'm turning the panel off *before* turning off the link.  The panel
goes nuts if you down the link before turning its power off; lots of
technicolor.

Downing the link doesn't require any communication with the panel, so
there's no issue with losing connectivity at this point:

	ironlake_edp_backlight_off(intel_dp);
	ironlake_edp_panel_off(intel_dp);               <= panel off

	/* Wake up the sink first */
	ironlake_edp_panel_vdd_on(intel_dp);
	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
	intel_dp_link_down(intel_dp);                   <= link down
	ironlake_edp_panel_vdd_off(intel_dp, false);

> But here it looks like you're shutting it off, then downing the link?
> Should this be reordered?

Nope, it's in the same order:

	ironlake_edp_backlight_off(intel_dp);
	ironlake_edp_panel_off(intel_dp);               <= panel off

	ironlake_edp_panel_vdd_on(intel_dp);
	intel_dp_sink_dpms(intel_dp, mode);
	intel_dp_link_down(intel_dp);                   <= link down
	ironlake_edp_panel_vdd_off(intel_dp, false);

The only difference in these two code paths is that dp_prepare turns the
sink to DPMS_ON, while dp_dpms turns the sink to DPMS_OFF.

-- 
keith.packard@...el.com

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