Re: [PATCH] mfd: motorola-cpcap: Do not hardcode SPI mode flags

[Linus Walleij <linus.walleij@linaro.org>]

On Thu, Dec 19, 2019 at 6:04 PM Tony Lindgren <tony@atomide.com> wrote:

> * Linus Walleij <linus.walleij@linaro.org> [700101 00:00]:
> > The current use of mode flags to us SPI_MODE_0 and
> > SPI_CS_HIGH is fragile: it overwrites anything already
> > assigned by the SPI core. Change it thusly:
> >
> > - Just |= the SPI_MODE_0 so we keep other flags
> > - Assign ^= SPI_CS_HIGH since we might be active high
> >   already, and that is usually the case with GPIOs used
> >   for chip select, even if they are in practice active low.
> >
> > Add a comment clarifying why ^= SPI_CS_HIGH is the right
> > choice here.
>
> Looks like this breaks booting for droid4 with a cpcap
> PMIC, probably as regulators won't work. There's no GPIO
> controller involved in this case for the chip select, the
> pins are directly controlled by the spi-omap2-mcspi.c
> driver.
>
> From the pin muxing setup we see there's a pull-down on
> mcspi1_cs0 pin meaning it's active high:
>
> /* 0x4a100138 mcspi1_cs0.mcspi1_cs0 ae23 */
> OMAP4_IOPAD(0x138, PIN_INPUT_PULLDOWN | MUX_MODE0)
>
> My guess a similar issue is with similar patches for
> all non-gpio spi controllers?
>
> Let me know if you want me to test some other changes,
> or if this patch depends on some other changes.

So this must mean that something else is setting SPI_CS_HIGH
for this driver, such as the device tree, right?

And the |= SPI_CS_HIGH assignment in the driver is just
surplus and we should just delete this code instead.

Would that be right?

Yours,
Linus Walleij