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

[Conor Dooley <conor@kernel.org>]

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On Thu, Oct 12, 2023 at 09:22:17AM +0000, Shravan.Chippa@microchip.com wrote:
> Hi,
> 
> > -----Original Message-----
> > From: Conor Dooley <conor@kernel.org>
> > Sent: Thursday, October 5, 2023 4:24 PM
> > To: Rob Herring <robh@kernel.org>
> > Cc: shravan Chippa - I35088 <Shravan.Chippa@microchip.com>;
> > green.wan@sifive.com; vkoul@kernel.org; krzysztof.kozlowski+dt@linaro.org;
> > palmer@dabbelt.com; paul.walmsley@sifive.com; conor+dt@kernel.org;
> > dmaengine@vger.kernel.org; devicetree@vger.kernel.org; linux-
> > riscv@lists.infradead.org; linux-kernel@vger.kernel.org; Nagasuresh Relli - I67208
> > <Nagasuresh.Relli@microchip.com>; Praveen Kumar - I30718
> > <Praveen.Kumar@microchip.com>; Conor Dooley - M52691
> > <Conor.Dooley@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@microchip.com>
> > > >
> > > > Add new compatible name microchip,mpfs-pdma to support out of order
> > > > dma transfers
> > > >
> > > > Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> > > > Signed-off-by: Shravan Chippa <shravan.chippa@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@c000000 {
>                 };
>                 pdma: dma-controller@3000000 {
> -                       compatible = "sifive,fu540-c000-pdma", "sifive,pdma0";
> +                       compatible = "microchip,mpfs-pdma", "sifive,fu540-c000-pdma", "sifive,pdma0";

This is gonna produce dtbs_check complaints. Your binding change only
permits `compatible = "microchip,mpfs-pdma", "sifive,pdma0";`

Cheers,
Conor.

>                         reg = <0x0 0x3000000 0x0 0x8000>;
>                         interrupt-parent = <&plic>;
>                         interrupts = <5 6>, <7 8>, <9 10>, <11 12>;
> ***************************

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