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

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Message-ID: <20180130100150.GB23047@ulmo>
Date:   Tue, 30 Jan 2018 11:01:50 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Dave Martin <dave.martin@....com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Yong Deng <yong.deng@...ewell.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Hugues Fruchet <hugues.fruchet@...com>,
        Yannick Fertre <yannick.fertre@...com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Ramesh Shanmugasundaram <ramesh.shanmugasundaram@...renesas.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Rick Chang <rick.chang@...iatek.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>, megous@...ous.com,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v6 2/2] media: V3s: Add support for Allwinner CSI.

On Tue, Jan 30, 2018 at 10:59:16AM +0100, Thierry Reding wrote:
> On Tue, Jan 30, 2018 at 10:24:48AM +0100, Arnd Bergmann wrote:
> > On Tue, Jan 30, 2018 at 8:54 AM, Maxime Ripard
> > <maxime.ripard@...e-electrons.com> 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@...aro.org> wrote:
> > >> > On Mon, Jan 29, 2018 at 9:25 AM, Maxime Ripard
> > >> > <maxime.ripard@...e-electrons.com> 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.
> 
> Yeah, I vaguely remember discussing something like this before. A quick
> search through my inbox yielded these two threads, mostly related to
> IOMMU but I think there were some mentions about dma-ranges and so on as
> well. I'll have to dig deeper into those threads to refresh my memories,
> but I won't get around to it until later today.
> 
> If someone wants to read up on this in the meantime, here are the links:
> 
> 	https://lkml.org/lkml/2014/4/27/346
> 	http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/257200.html
> 
> From a quick glance the issue of dma-ranges was something that we hand-
> waved at the time.
> 
> Thierry

Also found this, which seems to be relevant as well:

	http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/252715.html

Adding Dave.

Thierry

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