Re: [PATCH v2 7/9] dt-bindings: spi: mtk-snfi: Add read latch latency property

[AngeloGioacchino Del Regno]

Il 06/12/22 10:04, Xiangsheng Hou (侯祥胜) ha scritto:
> Hi Angelo,
>
> On Mon, 2022-12-05 at 15:21 +0100, AngeloGioacchino Del Regno wrote:
> > Il 05/12/22 07:57, Xiangsheng Hou ha scritto:
> > > Add mediatek,rx-latch-latency property which adjust read delay in
> > > the
> > > unit of clock cycle.
> > >
> > > Signed-off-by: Xiangsheng Hou <xiangsheng.hou@xxxxxxxxxxxx>
> > > Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > > ---
> > >    .../devicetree/bindings/spi/mediatek,spi-mtk-snfi.yaml     | 7
> > > +++++++
> > >    1 file changed, 7 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/spi/mediatek,spi-
> > > mtk-snfi.yaml b/Documentation/devicetree/bindings/spi/mediatek,spi-
> > > mtk-snfi.yaml
> > > index bab23f1b11fd..6e6ff8d73fcd 100644
> > > --- a/Documentation/devicetree/bindings/spi/mediatek,spi-mtk-
> > > snfi.yaml
> > > +++ b/Documentation/devicetree/bindings/spi/mediatek,spi-mtk-
> > > snfi.yaml
> > > @@ -45,6 +45,13 @@ properties:
> > >        description: device-tree node of the accompanying ECC engine.
> > >        $ref: /schemas/types.yaml#/definitions/phandle
> > >    
> > > +  mediatek,rx-latch-latency:
> > > +    description: Rx delay to sample data with this value, the
> > > value
> > > +                 unit is clock cycle.
> >
> > Can't we use nanoseconds or microseconds as a unit here, instead of
> > clock cycles?
>
> The clock cycle will be various with MediaTek SPI NAND controller which
> clock frequency can support 26/52/68/81/104MHz...
> It`s may be easy to configure and understand with clock cycle in unit.

Yes, but whatever clock frequency we use, the target is to always wait for
X nanoseconds, right?

Waiting for 5 clock cycles at 104MHz is obviously not the same as waiting
for the same 5 clock cycles at 26MHz: in that case, expressing the value
in nanoseconds or microseconds would make that independent from the
controller's clock frequency as the calculation from `time` to `cycles`
would be performed inside of the driver.

Regards,
Angelo