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

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Date:   Thu, 8 Dec 2022 09:46:26 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
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>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.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

On 08/12/2022 02:15, Xiangsheng Hou (侯祥胜) wrote:
>>>
>>> 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.

I am fine with this approach, but after explanations I was also fine
with clock cycles as unit. It's still quite specific unit and I think
several timings on buses are clock-cycle dependent, not time dependent.

Best regards,
Krzysztof