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

Conor Dooley
2023-10-05T10:54:57Z

[-- Attachment #1.1: Type: text/plain, Size: 2411 bytes --]

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.yaml
> > @@ -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.

Thanks,
Conor.

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]

[-- Attachment #2: Type: text/plain, Size: 161 bytes --]