Re: [RFC PATCH V1 1/6] dt-bindings: mt8183: Add binding for DIP shared memory

Frederic Chen
2019-05-07T14:22:05Z

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.

> > +
> > +- 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-dip_smem {
> > + compatible = "mediatek,reserve-memory-dip_smem";
> > + size = <0 0x1400000>;
> > + alignment = <0 0x1000>;
> > + alloc-ranges = <0 0x40000000 0 0x50000000>;
> > + };
> > + };
> > --
> > 2.18.0
> >

Sincerely,

Frederic Chen