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From:   Eric Anholt <eric@anholt.net>
To:     Kevin Quigley <kevin@kquigley.co.uk>,
        Andrzej Hajda <a.hajda@samsung.com>,
        "dri-devel\@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
Cc:     Boris Brezillon <boris.brezillon@bootlin.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        James Hughes <james.hughes@raspberrypi.org>,
        Archit Taneja <architt@codeaurora.org>
Subject: RE: [PATCH] drm/vc4: Enable the DSI module and link before other enables.
In-Reply-To: <C15157EF5067BD40AA5332C0BEB5F4D3079020E596F6@quiclu02.quigley.local>
References: <CGME20180604194448epcas1p29627759e2d8c0b1388c6700a7da77a45@epcas1p2.samsung.com> <20180604194437.13790-1-eric@anholt.net> <20180605082532eucas1p21328ec5bea7d588c81480829f862bdfd~1NhnMydDJ0562405624eucas1p2l@eucas1p2.samsung.com> <C15157EF5067BD40AA5332C0BEB5F4D3079020E596F6@quiclu02.quigley.local>
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Date:   Thu, 21 Jun 2018 16:19:24 -0700
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Kevin Quigley <kevin@kquigley.co.uk> writes:

> Hi,
>
> When we talk about control bus enable and video transfer enable for
> DSI, there is a mode in which control commands can be sent,
> interleaved with the video.  This is often done at the end-of-frame
> and/or end of line.  I've seen this handled in some other DSI device
> drivers.  In these cases, the driver has to look at the frame timing
> in the video and carefully select the number of control bytes which
> can be sent during the blanking periods.  The number of bytes which
> can be sent, is very much dependant on the panel-size and clock
> frequencies... (which determines the blanking time).  I'm not sure how
> widely this is a feature in the DSI encoder HW, and/or implemented
> purely in the drivers.

That scheduling is done by the VC4 DSI encoder.

> To conclude: I think that DSI encoder devices need to be able to
> support sending control data (LPDA) - concurrently with video frames.

I believe that should work already.

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