linux-kernel - Re: [PATCH 0/5] media: Allwinner A10 CSI support

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Date:   Thu, 15 Nov 2018 20:10:31 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Hans Verkuil <hans.verkuil@...co.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
Subject: Re: [PATCH 0/5] media: Allwinner A10 CSI support

Hi,

On Wed, Nov 14, 2018 at 11:24:48AM +0800, Chen-Yu Tsai wrote:
> On Tue, Nov 13, 2018 at 4:24 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > Here is a series introducing the support for the A10 (and SoCs of the same
> > generation) CMOS Sensor Interface (called CSI, not to be confused with
> > MIPI-CSI, which isn't support by that IP).
> >
> > That interface is pretty straightforward, but the driver has a few issues
> > that I wanted to bring up:
> >
> >   * The only board I've been testing this with has an ov5640 sensor
> >     attached, which doesn't work with the upstream driver. Copying the
> >     Allwinner init sequence works though, and this is how it has been
> >     tested. Testing with a second sensor would allow to see if it's an
> >     issue on the CSI side or the sensor side.
> >   * When starting a capture, the last buffer to capture will fail due to
> >     double buffering being used, and we don't have a next buffer for the
> >     last frame. I'm not sure how to deal with that though. It seems like
> >     some drivers use a scratch buffer in such a case, some don't care, so
> >     I'm not sure which solution should be preferred.
> >   * We don't have support for the ISP at the moment, but this can be added
> >     eventually.
> >
> >   * How to model the CSI module clock isn't really clear to me. It looks
> >     like it goes through the CSI controller and then is muxed to one of the
> >     CSI pin so that it can clock the sensor. I'm not quite sure how to
> >     model it, if it should be a clock, the CSI driver being a clock
> >     provider, or if the sensor should just use the module clock directly.
> 
> Which clock are you talking about? MCLK? This seems to be fed directly from
> the CCU, as there doesn't seem to be controls for it within the CSI hardware
> block, and the diagram doesn't list it either. IMO you don't have to model it.
> The camera sensor device node would just take a reference to it directly.

Yeah, that what I went for, I guess we agree :)

> You would probably enable the (separate) pinmux setting in the CSI
> controller node.

I'll change that.

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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