On Wed, 2022-12-07 at 10:48 +0100, AngeloGioacchino Del Regno wrote:

Il 07/12/22 03:00, Xiangsheng Hou (侯祥胜) ha scritto:

quoted

Hi Angelo,

On Tue, 2022-12-06 at 13:19 +0100, AngeloGioacchino Del Regno
wrote:

quoted

quoted

quoted

quoted

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.

There have two rx related timing properties in spi-peripheral-
props.
The rx-sample-delay-ns have been used in Mediatek snfi driver to
adjust
controller sample delay.
However another spi-rx-delay-us is in microseconds. Take 52MHz for
example, the clock cycle will be 19.23ns which lower than 1us. This
may
not easy to by one clock cycle.

I agree, but nothing prevents you from adding your own property for
that.

I propose "mediatek,rx-latch-latency-ns" or "mediatek,rx-latency-ns", 
so that
we can specify the delay in nanoseconds: in that case, when we
specify 19ns,
the driver will safely round that resulting in 52MHz == 19.23ns =>
19ns valid.

Will be fixed in next series.

Thanks
Xiangsheng Hou
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