Re: [PATCH v6 2/2] media: V3s: Add support for Allwinner CSI.

From: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
To: Maxime Ripard
	<maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
Cc: Linus Walleij
	<linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
	Yong Deng <yong.deng-+3dxTMOEIRNWk0Htik3J/w@public.gmane.org>,
	Mauro Carvalho Chehab
	<mchehab-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
	Chen-Yu Tsai <wens-jdAy2FN1RRM@public.gmane.org>,
	"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	Greg Kroah-Hartman
	<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
	Hans Verkuil
	<hans.verkuil-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>,
	Randy Dunlap <rdunlap-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	Stanimir Varbanov
	<stanimir.varbanov-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
	Hugues Fruchet <hugues.fruchet-qxv4g6HH51o@public.gmane.org>,
	Yannick Fertre <yannick.fertre-qxv4g6HH51o@public.gmane.org>,
	Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>,
	Benjamin Gaignard
	<benjamin.gaignard-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
	Ramesh Shanmugasundaram
	<ramesh.shanmugasundaram-kTT6dE0pTRh9uiUsa/gSgQ@public.gmane.org>,
	Sakari Ailus
	<sakari.ailus-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>,
	Rick Chang <rick.chang-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>,
	Linux Media Mailing List
	<linux-media-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS
Subject: Re: [PATCH v6 2/2] media: V3s: Add support for Allwinner CSI.
Date: Tue, 30 Jan 2018 10:24:48 +0100	[thread overview]
Message-ID: <CAK8P3a0QxQE=GM=SGPtT82=UreiqsgY6uMThvQ_woA3rjK0zjA@mail.gmail.com> (raw)
In-Reply-To: <20180130075441.rqxzkwero6sdfak6-ZC1Zs529Oq4@public.gmane.org>

On Tue, Jan 30, 2018 at 8:54 AM, Maxime Ripard
<maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org> wrote:
> On Mon, Jan 29, 2018 at 03:34:02PM +0100, Arnd Bergmann wrote:
>> On Mon, Jan 29, 2018 at 10:25 AM, Linus Walleij
>> <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
>> > On Mon, Jan 29, 2018 at 9:25 AM, Maxime Ripard
>> > <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org> wrote:
>> >> On Sat, Jan 27, 2018 at 05:14:26PM +0100, Linus Walleij wrote:

>>
>> At one point we had discussed adding a 'dma-masters' property that
>> lists all the buses on which a device can be a dma master, and
>> the respective properties of those masters (iommu, coherency,
>> offset, ...).
>>
>> IIRC at the time we decided that we could live without that complexity,
>> but perhaps we cannot.
>
> Are you talking about this ?
> https://elixir.free-electrons.com/linux/latest/source/Documentation/devicetree/bindings/dma/dma.txt#L41
>
> It doesn't seem to be related to that issue to me. And in our
> particular cases, all the devices are DMA masters, the RAM is just
> mapped to another address.

No, that's not the one I was thinking of. The idea at the time was much
more generic, and not limited to dma engines. I don't recall the details,
but I think that Thierry was either involved or made the proposal at the
time.

       Arnd