linux-kernel - Re: [PATCH 07/11] dt-bindings: spi: spi-nxp-fspi: add a new property nxp,fspi-dll-slvdly

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Date:   Tue, 05 Jul 2022 16:06:02 +0200
From:   Michael Walle <michael@...le.cc>
To:     Han Xu <han.xu@....com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Bough Chen <haibo.chen@....com>, ashish.kumar@....com,
        yogeshgaur.83@...il.com, broonie@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, singh.kuldeep87k@...il.com,
        tudor.ambarus@...rochip.com, p.yadav@...com,
        miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-mtd@...ts.infradead.org,
        festevam@...il.com, dl-linux-imx <linux-imx@....com>,
        linux-arm-kernel@...ts.infradead.org, zhengxunli@...c.com.tw
Subject: Re: [PATCH 07/11] dt-bindings: spi: spi-nxp-fspi: add a new property
 nxp,fspi-dll-slvdly

Am 2022-07-05 16:00, schrieb Han Xu:
>> -----Original Message-----
>> From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> Sent: Tuesday, July 5, 2022 8:29 AM
>> To: Han Xu <han.xu@....com>; Bough Chen <haibo.chen@....com>;
>> ashish.kumar@....com; yogeshgaur.83@...il.com; broonie@...nel.org;
>> robh+dt@...nel.org; krzysztof.kozlowski+dt@...aro.org;
>> singh.kuldeep87k@...il.com; tudor.ambarus@...rochip.com; 
>> p.yadav@...com;
>> michael@...le.cc; miquel.raynal@...tlin.com; richard@....at; 
>> vigneshr@...com;
>> shawnguo@...nel.org; s.hauer@...gutronix.de; kernel@...gutronix.de
>> Cc: linux-spi@...r.kernel.org; linux-kernel@...r.kernel.org;
>> devicetree@...r.kernel.org; linux-mtd@...ts.infradead.org; 
>> festevam@...il.com;
>> dl-linux-imx <linux-imx@....com>; 
>> linux-arm-kernel@...ts.infradead.org;
>> zhengxunli@...c.com.tw
>> Subject: Re: [PATCH 07/11] dt-bindings: spi: spi-nxp-fspi: add a new 
>> property
>> nxp,fspi-dll-slvdly
>> 
>> On 05/07/2022 15:19, Han Xu wrote:
>>>>>>> +  nxp,fspi-dll-slvdly:
>>>>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>>>>> +    description: |
>>>>>>> +      Specify the DLL slave line delay value.
>>>>>> 
>>>>>> What are the units?
>>>>> 
>>>>> Do you mean here need to give more detail explain about this 
>>>>> properity?
>>>>> 
>>>>> How about change like this?
>>>>>    Specify the DLL slave line delay value. The delay target for 
>>>>> slave delay line is:
>>>> ((nxp,fspi-dll-slvdly+1) * 1/32 * clock cycle of reference clock 
>>>> (serial root clock).
>>>> 
>>>> This would be good.
>>>> 
>>>>> The range of this value is 0~16.
>>>> 
>>>> This needs to go to schema instead as "maximum: 16".
>>>> 
>>>> But still the question is - what are the units used in this "delay"? 
>>>> ms? us?
>>> 
>>> HI Krzysztof,
>>> 
>>> According to the formula, the range should be 0~15, 16 should do 
>>> nothing or no
>> delay.
>> 
>> Sure, just add some constraint.
>> 
>>> 
>>> The unit should be clock phase. In other words, the delay can be in 
>>> range of
>> 1/32~1/2 clock cycle.
>> 
>> So we probably misunderstood each other... looking at the driver it 
>> also explains
>> the confusing. You encoded here register value which is pretty often 
>> wrong
>> approach.
>> 
>> This should be instead meaningful value for the user of the bindings, 
>> so usually
>> using one of property units:
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com
>> %2Fdevicetree-org%2Fdt-
>> schema%2Fblob%2Fmain%2Fdtschema%2Fschemas%2Fproperty-
>> units.yaml&amp;data=05%7C01%7Chan.xu%40nxp.com%7C0ffe3d706e064f14382
>> 108da5e8a5add%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C6379262
>> 45564450475%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV
>> 2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=Q4
>> SfVnBN%2BQ0vYKJzRf%2FXZkCA1WGyPV9doFcb%2BLSKx4w%3D&amp;reserved=0

Hm, you should fix your mail server.

>> 
>> I think you could use here clock cycles or clock phase, but then it 
>> has to be obvious
>> it is that unit.
> 
> Hi Krzysztof,
> 
> Let me clarify it, in the document a term "delay cell" was used to
> descript this register bit. Each delay cell equals "1/32 clock phase",
> so the unit of delay cell is clock phase. The value user need set in
> DT just number to define how many delay cells needed.

Then should the unit be "-degrees" and the possible range 0-180?

-michael