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

[Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>]

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.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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