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

[Greg Ungerer]

Hi Uwe,

On 21/03/17 22:11, Uwe Kleine-König wrote:
> On Tue, Mar 21, 2017 at 09:53:52PM +1000, Greg Ungerer wrote:
>> On 21/03/17 18:05, Uwe Kleine-König wrote:
>>> On Tue, Mar 21, 2017 at 12:05:20PM +1000, Greg Ungerer wrote:
>>>> On 20/03/17 23:22, Vladimir Zapolskiy wrote:
>>>>> For that type of bindings locally I have a hackish spi-imx driver change,
>>>>> which supports this option, but I'm unsure if it is universal enough.
>>>>
>>>> Do you mean supporting no cs-gpios tag?
>>>> That would be nice, but it would seem not many users of this are
>>>> using native chip selects.
>>>
>>> The reason for this is that the native chip selects are less flexible
>>> than gpios because you cannot control when they deassert. IIRC they do
>>> it too much for some chips. So the only reason to stick to them is that
>>> on some SoCs not all pins have a GPIO function. Not sure if transfer
>>> speed is another reason, but I would expect that the gain isn't that
>>> big.
>>
>> For the particular SPI device I am using, a Silicon Labs 32260,
>> it actually wants the assertion and de-assertion of the chip-select
>> between each byte. So it is the only way it can work for me.
>
> That should be doable with gpio-cs, too. You just need the right flags
> in your spi transfer IIRC.

Do you know which flag(s)  do that?

Regards
Greg