linux-kernel - Re: [PATCH v2 1/4] drm/i915/gen9: Only copy WM results for changed pipes to skl

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Message-ID: <8ad1925e-3bad-0d8d-f80d-f8d152c2531f@linux.intel.com>
Date:	Mon, 25 Jul 2016 15:01:02 +0200
From:	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:	Lyude <cpaul@...hat.com>, intel-gfx@...ts.freedesktop.org,
	Matt Roper <matthew.d.roper@...el.com>
Cc:	stable@...r.kernel.org,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Radhakrishna Sripada <radhakrishna.sripada@...el.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] drm/i915/gen9: Only copy WM results for changed
 pipes to skl_hw

Op 21-07-16 om 21:23 schreef Lyude:
> From: Matt Roper <matthew.d.roper@...el.com>
>
> When we write watermark values to the hardware, those values are stored
> in dev_priv->wm.skl_hw.  However with recent watermark changes, the
> results structure we're copying from only contains valid watermark and
> DDB values for the pipes that are actually changing; the values for
> other pipes remain 0.  Thus a blind copy of the entire skl_wm_values
> structure will clobber the values for unchanged pipes...we need to be
> more selective and only copy over the values for the changing pipes.
>
> This mistake was hidden until recently due to another bug that caused us
> to erroneously re-calculate watermarks for all active pipes rather than
> changing pipes.  Only when that bug was fixed was the impact of this bug
> discovered (e.g., modesets failing with "Requested display configuration
> exceeds system watermark limitations" messages and leaving watermarks
> non-functional, even ones initiated by intel_fbdev_restore_mode).
>
> Changes since v1:
>  - Add a function for copying a pipe's wm values
>    (skl_copy_wm_for_pipe()) so we can reuse this later
Looks like I can hit this when I wrote some tests for patch 2 in this series.

testcase will be kms_cursor_legacy.2x-flip-vs-cursor-legacy, but I haven't committed the changes yet.