Re: [RFC PATCH] dt-bindings: display: ti,tfp410.txt: convert to yaml

Tomi Valkeinen
2020-04-28T09:49:55Z

On 28/04/2020 12:20, Ricardo Cañuelo wrote:

> 2) The definition of ti,deskew in the original binding seems to be
> tailored to the current driver and the way it's defined may not be very
> DT-friendly.
>
> This parameter maps to a 3-bit field in a hardware register that takes
> a value from 0 to 7, so the [-4, 3] range described for this would map
> to [000, 111]: -4 -> 000, -3 -> 001, -2 -> 010, ... 3 -> 111.
>
> Then, the driver parses the parameter (unsigned) and casts it to a
> signed integer to get a number in the [-4, 3] range.

Interestingly the current example has ti,deskew = <4>...

> A vendor-specific property must have a type definition in json-schema,
> so if I translate the original bindings semantics directly, I should
> define ti,deskew as an int32, but this makes dt_binding_check fail if
> the property has a negative value in the example because of the
> internal representation of cells as unsigned integers:
>
> ti,deskew:0:0: 4294967293 is greater than the maximum of 2147483647

I don't quite understand this. We cannot have negative numbers in dts files? Or we can, but
dt_binding_check doesn't handle them correctly? Or that int32 is not supported in yaml bindings?

> So I can think of two solutions to this:
>
> a) Keep the ti,deskew property as an uint32 and document the valid
> range ([-4, 3]) in the property description (this is what this patch
> does currently).
>
> b) Redefine this property to be closer to the datasheet description
> (ie. unsigned integers from 0 to 7) and adapt the driver accordingly.
> This would also let us define its range properly using minimum and
> maximum properties for it.
>
> I think (b) is the right thing to do but I want to know your
> opinion. Besides, I don't have this hardware at hand and if I updated
> the driver I wouldn't be able to test it.

I don't think anyone has used deskew property, so I guess changing it is not out of the question.

Laurent, did you have a board that needs deskew when you added it to tfp410?

Tomi

--
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki