On Thu, May 16, 2019 at 1:12 AM Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote: > > On Wed, May 15, 2019 at 1:19 AM Rob Herring <robh@xxxxxxxxxx> wrote: > > > > On Tue, May 7, 2019 at 9:22 AM Frederic Chen <frederic.chen@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> > > > > > --- > > > > > .../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
