Re: [RFC PATCH V0 1/7] [media] dt-bindings: mt8183: Add binding for DIP shared memory

[Frederic Chen <frederic.chen@mediatek.com>]

Dear Laurent and Sakari,

I appreciate your messages.

On Sat, 2019-02-09 at 20:17 +0200, Laurent Pinchart wrote:
> On Sat, Feb 09, 2019 at 05:59:07PM +0200, Sakari Ailus wrote:
> > Hi Frederic,
> > 
> > Could you cc the devicetree list, please?
> > 
> > On Fri, Feb 01, 2019 at 07:21:25PM +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 0000000..0ded478
> > > --- /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)
> > 
> > What kind of purpose is the memory used for? Buffers containing video data,
> > or something else? Could the buffer objects be mapped on the devices
> > based on the need instead?

The memory buffers contain camera 3A tuning data, which are used by the
co-processor and DIP IP. About mapping the buffer based on the need
instead, I’m not sure I understand this point. Do you mean that
allocating and mapping the memory dynamically?

> 
> And could CMA be used when physically contiguous memory is needed ?

DIP driver does not use CMA now, because the first version will be used
by CrOS but CrOS won’t enable CMA.

> 
> > > +
> > > +
> > > +Required properties:
> > > +
> > > +- compatible: must be "mediatek,reserve-memory-dip_smem"
> > > +
> > > +- 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
> > > +
> > > +- size: required for dynamic allocation. The unit is bytes.
> > > +  If you want to enable the full feature of Digital Processing Unit,
> > > +  you need 20 MB at least.
> > > +
> > > +
> > > +Example:
> > > +
> > > +The following example shows the DIP shared memory setup for MT8183.
> > > +
> > > +	reserved-memory {
> > > +		#address-cells = <2>;
> > > +		#size-cells = <2>;
> > > +		ranges;
> > > +		reserve-memory-isp_smem {
> > > +			compatible = "mediatek,reserve-memory-dip_smem";
> > > +			size = <0 0x1400000>;
> > > +			alignment = <0 0x1000>;
> > > +			alloc-ranges = <0 0x40000000 0 0x50000000>;
> > > +		};
> > > +	};
> 

Sincerely,

Frederic Chen