Re: [PATCH v2 0/4] Support of MIPI CSI-2 for A83T

From: Maxime Ripard <maxime@cerno.tech>
To: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc: "Kévin L'hôpital" <kevin.lhopital@bootlin.com>,
	mark.rutland@arm.com, p.zabel@pengutronix.de,
	devicetree@vger.kernel.org, thomas.petazzoni@bootlin.com,
	linux-kernel@vger.kernel.org, sakari.ailus@linux.intel.com,
	wens@csie.org, robh+dt@kernel.org, hans.verkuil@cisco.com,
	yong.deng@magewell.com, mchehab+samsung@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v2 0/4] Support of MIPI CSI-2 for A83T
Date: Mon, 31 Aug 2020 15:04:38 +0200	[thread overview]
Message-ID: <20200831130438.5j237mntivrw3cwo@gilmour.lan> (raw)
In-Reply-To: <20200828141203.GC6858@aptenodytes>

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Hi Paul,

On Fri, Aug 28, 2020 at 04:12:03PM +0200, Paul Kocialkowski wrote:
> Hi everyone,
> 
> On Fri 28 Aug 20, 15:17, Kévin L'hôpital wrote:
> > This series adds the support for the MIPI CSI-2 controller for the A83T SoC.
> > The CSI controller is the same as the V3s SoC that's why I put the A83T
> > MIPI CSI-2 driver in sun6i-csi.
> > My work is based on the Allwinner BSP for A83T and also on MIPI CSI-2
> > specification for the A83T given by Allwinner.
> 
> To give a bit of context here, Kevin is our intern who worked on MIPI CSI-2
> support on the A83t this summer. As we were approaching the end of the
> internship, we wanted to publish the current state of the work as a working
> reference and base for mainline support.
> 
> However, we are well aware that there are significant design issues in this
> series, such as:
> - not supporting the fwnode graph;
> - not working with the DPHY API;
> - adding MIPI CSI-2 support under the same dt compatible as parallel CSI;
> 
> and probably other things.
> 
> Bootlin is currently working on V3s MIPI CSI-2 support and we intend to respin
> this series when submitting V3s MIPI CSI-2 support, with fixes to these design
> issues.

It's great to have that clarification, but it really doesn't address any
of the questions I had in the v1:

> There's a bunch of things that would need to be explained and / or
> argued for here, in particular:
>   - Why did you need to plumb it into sun6i-csi?
>   - You're naming the CSI part as the A83t CSI, while MIPI-CSI has been
>     supported since the A31(?), is there a reason for that?
>   - This is not documented anywhere, what did you base this work on?

You're also mentioning the v3s, without really stating why this driver
wouldn't be able to drive it.

> So we hope you keep this in mind when reviewing the series, which is
> not meant to be merged in its current state.

I mean, if the current code needs to be redesigned, and you provide no
details whatsoever on the hardware, I'm not really sure what kind of
input you're expecting.

Maxime

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