Re: [PATCH v1] spi: fix client driver breakages when using GPIO descriptors

Charles Keepax
2020-11-12T11:48:16Z

On Wed, Nov 11, 2020 at 11:24:14AM -0500, Sven Van Asbroeck wrote:
> On Wed, Nov 11, 2020 at 10:48 AM Mark Brown <broonie@kernel.org> wrote:
> >
> > Applied to
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next
>
> Thank you !
>
> Now that our minds are still focused on this subject, should
> commit 138c9c32f090 ("spi: spidev: Fix CS polarity if GPIO descriptors
> are used")
> be reverted?
>
> This fixed spidev to deal with SPI_CS_HIGH on gpiod.
> But after our fix, its behaviour will probably be broken again.
>
> Another candidate for revert is
> commit ada9e3fcc175 ("spi: dw: Correct handling of native chipselect")
> although I don't understand that code well enough to be sure.
>
> Adding Charles Keepax.

Looks like the code has changed a fair amount since my patch. The
important detail from it was trying to clarify the semantics of the
controller->set_cs callback. That function is called with a boolean
argument and that argument could have two possible meanings:

1) True means apply a high logic level to the chip select line.
2) True mean apply chip select.

Under interpretation 2) the chip select line would be set to a
different logic level depending on if the device is active high or
active low.

If I remember correctly at the point of my patch the core had just
changed between the two a couple of times but now consistently did 1)
(and looks like it still does), my patch intended to updated the
spi-dw driver to match that, as my SPI had stopped working. I think
it then turned out, my patch broke some other use-cases and that
the bit in the IP basically had 2) semantics in hardware. Which is
what this patch fixed:

commit 9aea644ca17b ("spi: dw: Fix native CS being unset")

After that patch my patch is mostly replaced so I don't think it
would make any sense to revert my patch at this point, and I
don't think your patch will break the spi-dw driver. I don't
have easy access to the hardware right now to test, but I will
give it is quick run when that option becomes available to me
again.

Your fix looks good to me, but I suspect you do need to fix the
spidev stuff although I have haven't looked at that in detail.

Thanks,
Charles