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Subject: Re: [PATCH v12 4/7] drm/i915/skl: Update plane watermarks atomically
 during plane updates
To: Lyude <cpaul@redhat.com>, intel-gfx@lists.freedesktop.org,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        Matt Roper <matthew.d.roper@intel.com>
References: <1471463761-26796-1-git-send-email-cpaul@redhat.com>
 <1471463761-26796-5-git-send-email-cpaul@redhat.com>
Cc: stable@vger.kernel.org, Daniel Vetter <daniel.vetter@intel.com>,
        Radhakrishna Sripada <radhakrishna.sripada@intel.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        David Airlie <airlied@linux.ie>, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Message-ID: <6048370c-fd04-4a73-8e79-44a90c08b1e4@linux.intel.com>
Date: Mon, 22 Aug 2016 13:24:11 +0200
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Op 17-08-16 om 21:55 schreef Lyude:
> Thanks to Ville for suggesting this as a potential solution to pipe
> underruns on Skylake.
>
> On Skylake all of the registers for configuring planes, including the
> registers for configuring their watermarks, are double buffered. New
> values written to them won't take effect until said registers are
> "armed", which is done by writing to the PLANE_SURF (or in the case of
> cursor planes, the CURBASE register) register.
>
> With this in mind, up until now we've been updating watermarks on skl
> like this:
This patch breaks on plane disabling. I think that all the disable_plane hooks
should zero all the watermark values. This might also make modeset more reliable

It's shown in this testcase that I wrote to expose this issue: kms_atomic_transition.plane-all-modeset-transition

I've applied patch 1, 2, 3 and 5 with some minor fixes.