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
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