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

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Message-ID: <9992c9a5-059a-9396-32ce-7ed63cd12a96@collabora.com>
Date:   Tue, 6 Dec 2022 13:19:51 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Xiangsheng Hou (侯祥胜) 
        <Xiangsheng.Hou@...iatek.com>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "gch981213@...il.com" <gch981213@...il.com>,
        "vigneshr@...com" <vigneshr@...com>,
        "richard@....at" <richard@....at>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Benliang Zhao (赵本亮) 
        <Benliang.Zhao@...iatek.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Bin Zhang (章斌) <bin.zhang@...iatek.com>
Subject: Re: [PATCH v2 7/9] dt-bindings: spi: mtk-snfi: Add read latch latency
 property

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@...iatek.com>
>>> Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>> ---
>>>    .../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