From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Herring 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: References: <20190417104511.21514-1-frederic.chen@mediatek.com> <20190417104511.21514-2-frederic.chen@mediatek.com> <20190430011506.GA8514@bogus> <1557238925.11663.21.camel@mtksdccf07> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Tomasz Figa Cc: Shik Chen , devicetree@vger.kernel.org, =?UTF-8?B?U2VhbiBDaGVuZyAo6YSt5piH5byYKQ==?= , Frederic Chen , =?UTF-8?B?UnlubiBXdSAo5ZCz6IKy5oGpKQ==?= , =?UTF-8?B?Q2hyaXN0aWUgWXUgKOa4uOmbheaDoCk=?= , srv_heupstream , =?UTF-8?B?SG9sbWVzIENoaW91ICjpgrHmjLop?= , suleiman@chromium.org, Jerry-ch Chen , yuzhao@chromium.org, =?UTF-8?B?SnVuZ28gTGluICjmnpfmmI7kv4op?= , Sj Huang , Laurent Pinchart , Hans Verkuil , zwisler@chromium.org, Matthias Brugger , "moderated list:ARM/Mediatek SoC support" , Mauro List-Id: devicetree@vger.kernel.org On Thu, May 16, 2019 at 1:12 AM Tomasz Figa wrote: > > On Wed, May 15, 2019 at 1:19 AM Rob Herring wrote: > > > > On Tue, May 7, 2019 at 9:22 AM Frederic Chen 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 > > > > > --- > > > > > .../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