[PATCH v2 2/4] dt-bindings: dma: sf-pdma: add new compatible name

[Shravan.Chippa at microchip.com]

Hi,

> -----Original Message-----
> From: Conor Dooley <conor at kernel.org>
> Sent: Thursday, October 5, 2023 4:24 PM
> To: Rob Herring <robh at kernel.org>
> Cc: shravan Chippa - I35088 <Shravan.Chippa at microchip.com>;
> green.wan at sifive.com; vkoul at kernel.org; krzysztof.kozlowski+dt at linaro.org;
> palmer at dabbelt.com; paul.walmsley at sifive.com; conor+dt at kernel.org;
> dmaengine at vger.kernel.org; devicetree at vger.kernel.org; linux-
> riscv at lists.infradead.org; linux-kernel at vger.kernel.org; Nagasuresh Relli - I67208
> <Nagasuresh.Relli at microchip.com>; Praveen Kumar - I30718
> <Praveen.Kumar at microchip.com>; Conor Dooley - M52691
> <Conor.Dooley at microchip.com>
> Subject: Re: [PATCH v2 2/4] dt-bindings: dma: sf-pdma: add new compatible
> name
> 
> On Wed, Oct 04, 2023 at 08:30:21AM -0500, Rob Herring wrote:
> > On Tue, Oct 03, 2023 at 09:52:13AM +0530, shravan chippa wrote:
> > > From: Shravan Chippa <shravan.chippa at microchip.com>
> > >
> > > Add new compatible name microchip,mpfs-pdma to support out of order
> > > dma transfers
> > >
> > > Reviewed-by: Conor Dooley <conor.dooley at microchip.com>
> > > Signed-off-by: Shravan Chippa <shravan.chippa at microchip.com>
> > > ---
> > >  .../bindings/dma/sifive,fu540-c000-pdma.yaml         | 12 ++++++++----
> > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> > > b/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> > > index a1af0b906365..974467c4bacb 100644
> > > ---
> > > a/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
> > > +++ b/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.y
> > > +++ aml
> > > @@ -27,10 +27,14 @@ allOf:
> > >
> > >  properties:
> > >    compatible:
> > > -    items:
> > > -      - enum:
> > > -          - sifive,fu540-c000-pdma
> > > -      - const: sifive,pdma0
> > > +    oneOf:
> > > +      - items:
> > > +          - const: microchip,mpfs-pdma # Microchip out of order DMA transfer
> > > +          - const: sifive,fu540-c000-pdma # Sifive in-order DMA
> > > + transfer
> 
> IIRC I asked for the comments here to be removed on the previous version, and
> my r-b was conditional on that.
> The device specific compatible has merit outside of the ordering, which may just
> be a software policy decision.
> 
> > This doesn't really make sense. microchip,mpfs-pdma is compatible with
> > sifive,fu540-c000-pdma and sifive,fu540-c000-pdma is compatible with
> > sifive,pdma0, but microchip,mpfs-pdma is not compatible with
> > sifive,pdma0? (Or replace "compatible with" with "a superset of")
> 
> TBH, I am not sure why it was done this way. Probably because the driver
> contains both sifive,pdma0 and sifive,fu540-c000-pdma. Doing compatible =
> "microchip,mpfs-pdma", "sifive,fu540-c000-pdma", "sifive,pdma0"; thing would
> be fine.
> 
> > Any fallback is only useful if an OS only understanding the fallback
> > will work with the h/w. Does this h/w work without the driver changes?
> 
> Yes.
> I've been hoping that someone from SiFive would come along, and in response to
> this patchset, tell us _why_ the driver does not make use of out-of-order transfers
> to begin with.
> 

I am also expecting a replay someone from SiFive
The out-of-order should work with other RISC-V platforms also.

I will try to send V3 with the below changes (just adding a new compatible name)

****************************
--- a/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
+++ b/Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml
@@ -29,6 +29,7 @@ properties:
   compatible:
     items:
       - enum:
+          - microchip,mpfs-pdma
           - sifive,fu540-c000-pdma
       - const: sifive,pdma0
     description:
***************************

Device tree patch
*****************************
--- a/arch/riscv/boot/dts/microchip/mpfs.dtsi
+++ b/arch/riscv/boot/dts/microchip/mpfs.dtsi
@@ -221,7 +221,7 @@ plic: interrupt-controller at c000000 {
                };
                pdma: dma-controller at 3000000 {
-                       compatible = "sifive,fu540-c000-pdma", "sifive,pdma0";
+                       compatible = "microchip,mpfs-pdma", "sifive,fu540-c000-pdma", "sifive,pdma0";
                        reg = <0x0 0x3000000 0x0 0x8000>;
                        interrupt-parent = <&plic>;
                        interrupts = <5 6>, <7 8>, <9 10>, <11 12>;
***************************

Thanks,
Shravan

> Thanks,
> Conor.