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

[Michael Walle]

Am 2022-07-05 16:00, schrieb Han Xu:
> > -----Original Message-----
> > From: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > Sent: Tuesday, July 5, 2022 8:29 AM
> > To: Han Xu <han.xu@xxxxxxx>; Bough Chen <haibo.chen@xxxxxxx>;
> > ashish.kumar@xxxxxxx; yogeshgaur.83@xxxxxxxxx; broonie@xxxxxxxxxx;
> > robh+dt@xxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx;
> > singh.kuldeep87k@xxxxxxxxx; tudor.ambarus@xxxxxxxxxxxxx; 
> > p.yadav@xxxxxx;
> > michael@xxxxxxxx; miquel.raynal@xxxxxxxxxxx; richard@xxxxxx; 
> > vigneshr@xxxxxx;
> > shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx
> > Cc: linux-spi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > devicetree@xxxxxxxxxxxxxxx; linux-mtd@xxxxxxxxxxxxxxxxxxx; 
> > festevam@xxxxxxxxx;
> > dl-linux-imx <linux-imx@xxxxxxx>; 
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > zhengxunli@xxxxxxxxxxx
> > 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