Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <d5f58e82-2644-3e16-f27a-de72ed8ab74d@linaro.org>
Date:   Thu, 8 Dec 2022 09:46:26 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.5.1
Subject: Re: [PATCH v2 7/9] dt-bindings: spi: mtk-snfi: Add read latch latency
 property
Content-Language: en-US
To:     =?UTF-8?B?WGlhbmdzaGVuZyBIb3UgKOS+r+elpeiDnCk=?= 
        <Xiangsheng.Hou@mediatek.com>,
        "miquel.raynal@bootlin.com" <miquel.raynal@bootlin.com>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "broonie@kernel.org" <broonie@kernel.org>,
        "krzysztof.kozlowski+dt@linaro.org" 
        <krzysztof.kozlowski+dt@linaro.org>,
        "matthias.bgg@gmail.com" <matthias.bgg@gmail.com>,
        "gch981213@gmail.com" <gch981213@gmail.com>,
        "vigneshr@ti.com" <vigneshr@ti.com>,
        "angelogioacchino.delregno@collabora.com" 
        <angelogioacchino.delregno@collabora.com>,
        "richard@nod.at" <richard@nod.at>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mediatek@lists.infradead.org" 
        <linux-mediatek@lists.infradead.org>,
        "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        =?UTF-8?B?QmVubGlhbmcgWmhhbyAo6LW15pys5LquKQ==?= 
        <Benliang.Zhao@mediatek.com>,
        "linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        =?UTF-8?B?QmluIFpoYW5nICjnq6Dmlowp?= <bin.zhang@mediatek.com>
References: <20221205065756.26875-1-xiangsheng.hou@mediatek.com>
 <20221205065756.26875-8-xiangsheng.hou@mediatek.com>
 <ce449a0c-efcc-0ac1-fb8e-c2b4148a5bc1@collabora.com>
 <a8f706b37f5decf91bfa9a9ac8cf04be4346dd85.camel@mediatek.com>
 <9992c9a5-059a-9396-32ce-7ed63cd12a96@collabora.com>
 <e2ccf42f94152ccacad3a2eaec234ae0566474ec.camel@mediatek.com>
 <b877af37-462e-c923-41c0-09c370062700@collabora.com>
 <97408c484927b6520ec79b23220496d628156e5f.camel@mediatek.com>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <97408c484927b6520ec79b23220496d628156e5f.camel@mediatek.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

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