Re: [PATCH 04/11] dt-bindings: dma: stm32-dma3: prevent linked-list refactoring

[Amelie Delaunay]

On 10/10/24 20:14, Rob Herring wrote:
> On Thu, Oct 10, 2024 at 04:27:54PM +0200, Amelie Delaunay wrote:
> > stm32-dma3 driver refactors the linked-list in order to address the memory
> > with the highest possible data width.
> > It means that it can introduce up to 2 linked-list items. One with a
> > transfer length multiple of channel maximum burst length and so with the
> > highest possible data width. And an extra one with the latest bytes, with
> > lower data width.
> > Some devices (e.g. FMC ECC) don't support having several transfers instead
> > of only one.
> > So add the possibility to prevent linked-list refactoring, by setting bit
> > 17 of the 'DMA transfer requirements' bit mask.
> >
> > Signed-off-by: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>
> > ---
> >   Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> > index 5484848735f8ac3d2050104bbab1d986e82ba6a7..38c30271f732e0c8da48199a224a88bb647eeca7 100644
> > --- a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> > +++ b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> > @@ -99,6 +99,9 @@ properties:
> >           -bit 16: Prevent packing/unpacking mode
> >             0x0: pack/unpack enabled when source data width/burst != destination data width/burst
> >             0x1: memory data width/burst forced to peripheral data width/burst to prevent pack/unpack
> > +        -bit 17: Prevent linked-list refactoring
> > +          0x0: don't prevent driver to refactor the linked-list for optimal performance
> > +          0x1: prevent driver to refactor the linked-list, despite not optimal performance
>
> Driver settings don't belong in DT. Perhaps reword it in terms of h/w
> constraints (i.e. single transfer limitation).

Thanks for the review and suggestion. I'll reword it in V2. Indeed, it 
is due to single transfer limitation, e.g. for ECC status registers 
transfer.

-bit 17: Prevent additional transfers due to linked-list refactoring
  0x0: don't prevent additional transfers for optimal performance
  0x1: prevent additional transfers to accommodate user constraints 
such as single transfer


Regards,
Amelie

> >   
> >   required:
> >     - compatible
> >
> > --
> > 2.25.1