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From: Rob Herring <robh@kernel.org>
To: Tomasz Figa <tfiga@chromium.org>
Cc: "Shik Chen" <shik@chromium.org>,
	devicetree@vger.kernel.org,
	"Sean Cheng (鄭昇弘)" <Sean.Cheng@mediatek.com>,
	"Frederic Chen" <frederic.chen@mediatek.com>,
	"Rynn Wu (吳育恩)" <Rynn.Wu@mediatek.com>,
	"Christie Yu (游雅惠)" <christie.yu@mediatek.com>,
	srv_heupstream <srv_heupstream@mediatek.com>,
	"Holmes Chiou (邱挺)" <holmes.chiou@mediatek.com>,
	suleiman@chromium.org,
	"Jerry-ch Chen" <Jerry-ch.Chen@mediatek.com>,
	yuzhao@chromium.org, "Jungo Lin (林明俊)" <jungo.lin@mediatek.com>,
	"Sj Huang" <sj.huang@mediatek.com>,
	"Laurent Pinchart" <laurent.pinchart+renesas@ideasonboard.com>,
	"Hans Verkuil" <hans.verkuil@cisco.com>,
	zwisler@chromium.org, "Matthias Brugger" <matthias.bgg@gmail.com>,
	"moderated list:ARM/Mediatek SoC support"
	<linux-mediatek@lists.infradead.org>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	"Linux Media Mailing List" <linux-media@vger.kernel.org>
Subject: Re: [RFC PATCH V1 1/6] dt-bindings: mt8183: Add binding for DIP shared memory
Date: Fri, 17 May 2019 17:22:41 -0500
Message-ID: <CAL_Jsq+hcgth5gT4gCKPiWtFvje8eOHFs1PxtkHJ6Raj8TOw3w@mail.gmail.com> (raw)
In-Reply-To: <CAAFQd5BVWjcxp9Tia9Pmgn_54bc9n5Vs1s__G7YWHiezfVVYpA@mail.gmail.com>

On Thu, May 16, 2019 at 1:12 AM Tomasz Figa <tfiga@chromium.org> wrote:
>
> On Wed, May 15, 2019 at 1:19 AM Rob Herring <robh@kernel.org> wrote:
> >
> > On Tue, May 7, 2019 at 9:22 AM Frederic Chen <frederic.chen@mediatek.com> wrote:
> > >
> > > Dear Rob,
> > >
> > > I appreciate your comments.
> > >
> > > On Mon, 2019-04-29 at 20:15 -0500, Rob Herring wrote:
> > > > On Wed, Apr 17, 2019 at 06:45:06PM +0800, Frederic Chen wrote:
> > > > > This patch adds the binding for describing the shared memory
> > > > > used to exchange configuration and tuning data between the
> > > > > co-processor and Digital Image Processing (DIP) unit of the
> > > > > camera ISP system on Mediatek SoCs.
> > > > >
> > > > > Signed-off-by: Frederic Chen <frederic.chen@mediatek.com>
> > > > > ---
> > > > >  .../mediatek,reserve-memory-dip_smem.txt      | 45 +++++++++++++++++++
> > > > >  1 file changed, 45 insertions(+)
> > > > >  create mode 100644 Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt b/Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt
> > > > > new file mode 100644
> > > > > index 000000000000..64c001b476b9
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt
> > > > > @@ -0,0 +1,45 @@
> > > > > +Mediatek DIP Shared Memory binding
> > > > > +
> > > > > +This binding describes the shared memory, which serves the purpose of
> > > > > +describing the shared memory region used to exchange data between Digital
> > > > > +Image Processing (DIP) and co-processor in Mediatek SoCs.
> > > > > +
> > > > > +The co-processor doesn't have the iommu so we need to use the physical
> > > > > +address to access the shared buffer in the firmware.
> > > > > +
> > > > > +The Digital Image Processing (DIP) can access memory through mt8183 IOMMU so
> > > > > +it can use dma address to access the memory region.
> > > > > +(See iommu/mediatek,iommu.txt for the detailed description of Mediatek IOMMU)
> > > > > +
> > > > > +
> > > > > +Required properties:
> > > > > +
> > > > > +- compatible: must be "mediatek,reserve-memory-dip_smem"
> > > >
> > > > Don't use '_'.
> > >
> > > I got it. I will use "mediatek,reserve-memory-dip-smem" instead in next
> > > version of the patch
> > >
> > > >
> > > > > +
> > > > > +- reg: required for static allocation (see reserved-memory.txt for
> > > > > +  the detailed usage)
> > > > > +
> > > > > +- alloc-range: required for dynamic allocation. The range must
> > > > > +  between 0x00000400 and 0x100000000 due to the co-processer's
> > > > > +  addressing limitation
> > > >
> > > > Generally, you should pick either static or dynamic allocation for a
> > > > given binding. Static if there's some address restriction or sharing,
> > > > dynamic if not.
> > > >
> > > > Sounds like static in this case.
> > > >
> > >
> > > DIP reserved memory has address restriction so it is the static case. I
> > > would like to remove the dynamic allocation part and modify the
> > > description as following:
> > >
> > > - reg: required for DIP. The range must be between 0x00000400 and
> > >   0x100000000 due to the co-processor's addressing limitation.
> > >   The size must be 26MB. Please see reserved-memory.txt for the
> > >   detailed usage.
> >
> > You can use dma-ranges to define addressing translations and
> > restrictions like this. That will in turn set the device's dma-mask to
> > ensure allocations are done in a region that is addressable.
> >
> > But if you have a known, fixed size, then a carve out with
> > reserved-memory is fine.
>
> There is also another aspect here. The coprocessor that we're
> allocating the memory for is behind an MPU that must be programmed
> completely in one go and locked for security reasons to ensure that
> the coprocessor itself doesn't rewrite the MPU settings. That means
> that we need to have all the allocations completed before booting that
> coprocessor.
>
> To be honest, I'd adopt a completely different design here.
>
> We're going to have a driver for that coprocessor (SCP) and IMHO any
> shared memory areas should belong to it. Then, any specific drivers
> talking to the firmware running on SCP should ask the SCP driver to
> allocate some memory from its fixed pool. WDYT?

That's more than just an address restriction, so yeah, use a
reserved-memory area.

Rob

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Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-17 10:45 [RFC PATCH V1 0/6] media: platform: Add support for Digital Image Processing (DIP) on mt8183 SoC Frederic Chen
2019-04-17 10:45 ` [RFC PATCH V1 1/6] dt-bindings: mt8183: Add binding for DIP shared memory Frederic Chen
2019-04-30  1:15   ` Rob Herring
2019-05-07 14:22     ` Frederic Chen
2019-05-14 16:19       ` Rob Herring
2019-05-16  6:12         ` Tomasz Figa
2019-05-17 22:22           ` Rob Herring [this message]
2019-04-17 10:45 ` [RFC PATCH V1 2/6] dts: arm64: mt8183: Add DIP shared memory node Frederic Chen
2019-04-17 10:45 ` [RFC PATCH V1 3/6] dt-bindings: mt8183: Added DIP dt-bindings Frederic Chen
2019-04-30  1:16   ` Rob Herring
2019-05-07 14:16     ` Frederic Chen
2019-05-14 16:14       ` Rob Herring
2019-04-17 10:45 ` [RFC PATCH V1 4/6] dts: arm64: mt8183: Add DIP nodes Frederic Chen
2019-04-17 10:45 ` [RFC PATCH V1 5/6] media: platform: Add Mediatek DIP driver KConfig Frederic Chen
     [not found] ` <20190417104511.21514-7-frederic.chen@mediatek.com>
2019-05-22  9:51   ` [RFC PATCH V1 6/6] platform: mtk-isp: Add Mediatek DIP driver Shik Chen
2019-05-23 14:24     ` Frederic Chen
     [not found]   ` <20190509094846.GA65444@google.com>
     [not found]     ` <1558466055.15388.342.camel@mtksdccf07>
2019-05-22 10:25       ` Tomasz Figa
2019-05-23 13:46         ` Frederic Chen

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