linux-kernel - Re: [PATCH 6/7] drm/exynos/decon5433: signal vblank only on odd fields

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Message-id: <953193f0-484e-0457-baf4-e42b44a3f147@samsung.com>
Date:   Mon, 23 Jan 2017 10:15:16 +0100
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Inki Dae <inki.dae@...sung.com>, dri-devel@...ts.freedesktop.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-samsung-soc@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-kernel@...r.kernel.org,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 6/7] drm/exynos/decon5433: signal vblank only on odd fields

On 20.01.2017 14:55, Ville Syrjälä wrote:
> On Fri, Jan 20, 2017 at 07:52:24AM +0100, Andrzej Hajda wrote:
>> In case of interlace mode irq is generated for odd and even fields, but
>> vblank should be signaled only for the last emitted field.
> I'm pretty sure most drivers signal it for both fields. At least i915
> does.

The question is which behavior is correct? I have not found any clear
statement in the documentation, or drm core code.
I have guessed that since vblank event is used to signal end of scan-out
of buffer it should be called after scan-out of whole buffer - in case
of interlaced mode after scan-out of 2nd field.
Maybe my assumption is wrong, in such case this patch should be dropped
and mixer driver also should be fixed, but before doing that it would be
good to know for sure how it should be handled correctly.

Regards
Andrzej