Re: [PATCHv3 1/2] spi: imx: fix use of native chip-selects with devicetree

[Oleksij Rempel <ore-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

On 10.08.2017 13:35, Greg Ungerer wrote:
> On 10/08/17 19:35, Vladimir Zapolskiy wrote:
>> Hi Oleksij,
>>
...
>>
>> Errors in DTB (or platform data) may confuse a driver and lead to runtime
>> misbehaviour. You describe an error in a board DTB, which is definitely
>> better to handle in the SPI driver, but I don't think it is strictly
>> mandatory to do it, because DTB errors are supposed to be fixed in DTB.
>>
>> May be one day a formal check of DTBs against Documentation/devicetree
>> descriptions will be added and such DTB errors could be captured on DTB
>> compilation stage.
>
> I completely agree with Vladmir here. Since "cs-gpios" defines the
> number of chip selects, as per the code you point out, it is the range
> limit. So if a DTB defines it wrongly then you can expect some things
> not to work right. The spi code quite rightly relies on the DTB
> definitions to be correct for proper operation.
>
>
>>> And in this case:
>>> cs-gpios = <&gpio1 0 0>, <&gpio1 1 0>, <&gpio1 2 0>, <&gpio1 3 0>, <0>;
>>>
>>> we should produce a 3 bit value b100 which will be shifted left and
>>> "or"-ed with other ctrl bits.
>
> So the register settings will be wrong and the device will not work.
> You can't really expect any other behavior from an incorrect DTB.

Ok :)
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