[PATCH] spi: spidev: Fix CS polarity if GPIO descriptors are used

[PATCH] spi: spidev: Fix CS polarity if GPIO descriptors are used

[Lukas Wunner]

Commit f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
amended of_spi_parse_dt() to always set SPI_CS_HIGH for SPI slaves whose
Chip Select is defined by a "cs-gpios" devicetree property.

This change broke userspace applications which issue an SPI_IOC_WR_MODE
ioctl() to an spidev:  Chip Select polarity will be incorrect unless the
application is changed to set SPI_CS_HIGH.  And once changed, it will be
incompatible with kernels not containing the commit.

Fix by setting SPI_CS_HIGH in spidev_ioctl() (under the same conditions
as in of_spi_parse_dt()).

Fixes: f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
Reported-by: Simon Han <z.han-pnUOlEj4XnTQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>
Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org # v5.1+
Cc: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
---
 drivers/spi/spidev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index 1e217e3e9486..2ab6e782f14c 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -396,6 +396,7 @@ spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		else
 			retval = get_user(tmp, (u32 __user *)arg);
 		if (retval == 0) {
+			struct spi_controller *ctlr = spi->controller;
 			u32	save = spi->mode;
 
 			if (tmp & ~SPI_MODE_MASK) {
@@ -403,6 +404,10 @@ spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 				break;
 			}
 
+			if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
+			    ctlr->cs_gpiods[spi->chip_select])
+				tmp |= SPI_CS_HIGH;
+
 			tmp |= spi->mode & ~SPI_MODE_MASK;
 			spi->mode = (u16)tmp;
 			retval = spi_setup(spi);
-- 
2.24.0

Re: [PATCH] spi: spidev: Fix CS polarity if GPIO descriptors are used

[Linus Walleij]

On Tue, Feb 18, 2020 at 1:08 PM Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org> wrote:

> Commit f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
> amended of_spi_parse_dt() to always set SPI_CS_HIGH for SPI slaves whose
> Chip Select is defined by a "cs-gpios" devicetree property.
>
> This change broke userspace applications which issue an SPI_IOC_WR_MODE
> ioctl() to an spidev:  Chip Select polarity will be incorrect unless the
> application is changed to set SPI_CS_HIGH.  And once changed, it will be
> incompatible with kernels not containing the commit.
>
> Fix by setting SPI_CS_HIGH in spidev_ioctl() (under the same conditions
> as in of_spi_parse_dt()).
>
> Fixes: f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
> Reported-by: Simon Han <z.han-pnUOlEj4XnTQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>
> Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org # v5.1+
> Cc: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
(...)

Nit: I would also insert a comment in the code to tell what is going on.

> +                       if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
> +                           ctlr->cs_gpiods[spi->chip_select])
> +                               tmp |= SPI_CS_HIGH;

Should this be tmp ^= SPI_CS_HIGH?

If the device tree node for cs-gpios is actually active high, which
happens, then you probably want the opposite of what was
requested, right?

Yours,
Linus Walleij

Re: [PATCH] spi: spidev: Fix CS polarity if GPIO descriptors are used

[Lukas Wunner]

On Wed, Feb 19, 2020 at 04:47:50PM +0100, Linus Walleij wrote:
> On Tue, Feb 18, 2020 at 1:08 PM Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org> wrote:
> > Commit f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
> > amended of_spi_parse_dt() to always set SPI_CS_HIGH for SPI slaves whose
> > Chip Select is defined by a "cs-gpios" devicetree property.
> >
> > This change broke userspace applications which issue an SPI_IOC_WR_MODE
> > ioctl() to an spidev:  Chip Select polarity will be incorrect unless the
> > application is changed to set SPI_CS_HIGH.  And once changed, it will be
> > incompatible with kernels not containing the commit.
> >
> > Fix by setting SPI_CS_HIGH in spidev_ioctl() (under the same conditions
> > as in of_spi_parse_dt()).
> 
> Nit: I would also insert a comment in the code to tell what is going on.

Fair enough, but the below should be clarified before I respin:


> > +                       if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
> > +                           ctlr->cs_gpiods[spi->chip_select])
> > +                               tmp |= SPI_CS_HIGH;
> 
> Should this be tmp ^= SPI_CS_HIGH?
> 
> If the device tree node for cs-gpios is actually active high, which
> happens, then you probably want the opposite of what was
> requested, right?

I don't quite follow.  Using an XOR here would seem to be inconsistent
with what you added to of_spi_parse_dt():  In that function, you
*always* set SPI_CS_HIGH if gpio_descs are used.  So if the polarity
is specified in the cs-gpios property, anything else is considered
irrelevant and ignored.

Applying the same logic to spidev_ioctl() means that if the user
specified SPI_CS_HIGH, it is likewise ignored because the polarity
in the cs-gpios property takes precedence.  Am I missing something?

TBH the way commit f3186dd87669 abuses SPI_CS_HIGH seems clumsy to me.
Would it not have been possible to just amend spi_set_cs() like this:

-	if (spi->mode & SPI_CS_HIGH)
+	if (spi->mode & SPI_CS_HIGH && !(ctlr->use_gpio_descriptors &&
+					 ctlr->cs_gpiods &&
+					 ctlr->cs_gpiods[spi->chip_select]))
		enable = !enable;

This would have avoided the regression fixed by my patch.
Also note that spi_setup() emits a dev_dbg() which now incorrectly
reports "cs_high" if a cs-gpios property is present. :-(

Thanks,

Lukas

Re: [PATCH] spi: spidev: Fix CS polarity if GPIO descriptors are used

[Lukas Wunner]

On Thu, Feb 20, 2020 at 07:11:22AM +0100, Lukas Wunner wrote:
> -	if (spi->mode & SPI_CS_HIGH)
> +	if (spi->mode & SPI_CS_HIGH && !(ctlr->use_gpio_descriptors &&
> +					 ctlr->cs_gpiods &&
> +					 ctlr->cs_gpiods[spi->chip_select]))
> 		enable = !enable;

Sorry, I meant (spi->mode & SPI_CS_HIGH || (ctlr->...)
                                        ^^^^

Re: [PATCH] spi: spidev: Fix CS polarity if GPIO descriptors are used

[Linus Walleij]

On Thu, Feb 20, 2020 at 7:11 AM Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org> wrote:
> On Wed, Feb 19, 2020 at 04:47:50PM +0100, Linus Walleij wrote:

> > > +                       if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
> > > +                           ctlr->cs_gpiods[spi->chip_select])
> > > +                               tmp |= SPI_CS_HIGH;
> >
> > Should this be tmp ^= SPI_CS_HIGH?
> >
> > If the device tree node for cs-gpios is actually active high, which
> > happens, then you probably want the opposite of what was
> > requested, right?
>
> I don't quite follow.  Using an XOR here would seem to be inconsistent
> with what you added to of_spi_parse_dt():  In that function, you
> *always* set SPI_CS_HIGH if gpio_descs are used.  So if the polarity
> is specified in the cs-gpios property, anything else is considered
> irrelevant and ignored.

It's not just cs-gpios though: if you look in drivers/gpio/gpiolib-of.c
in the function of_gpio_flags_quirks() you see that the bool property
spi-cs-high in the consumer node will take precedence over the
cs-gpios property and that will also be handled transparently by gpiolib.
(commit 6953c57ab1721 with fixes on top).

But I guess that is what you mean.

Yes as far as I can see this solves the problem of double-specifying
(both in device tree and from userspace) that we want CS high,
so after some thinking:
Reviewed-by: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>

> TBH the way commit f3186dd87669 abuses SPI_CS_HIGH seems clumsy to me.

Clumsy programmer, that's me, yeah sometimes :/

> Would it not have been possible to just amend spi_set_cs() like this:
>
> -       if (spi->mode & SPI_CS_HIGH)
> +       if (spi->mode & SPI_CS_HIGH || (ctlr->use_gpio_descriptors &&
> +                                        ctlr->cs_gpiods &&
> +                                        ctlr->cs_gpiods[spi->chip_select]))
>                 enable = !enable;
>
> This would have avoided the regression fixed by my patch.

There is way too much double inversion going on for sure (some
of it dating back before any attempts to use gpiolib for polarity
handling and I just feel partially responsible) but I just haven't
figured out how to properly fix the problem. Maybe it was just
stupid of me to try to move polarity inversion semantics over to
gpiolib before fixing that though.

Patches like the above are also welcome!

Yours,
Linus Walleij

Applied "spi: spidev: Fix CS polarity if GPIO descriptors are used" to the spi tree

[Mark Brown]

The patch

   spi: spidev: Fix CS polarity if GPIO descriptors are used

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-5.6

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 138c9c32f090894614899eca15e0bb7279f59865 Mon Sep 17 00:00:00 2001
From: Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>
Date: Tue, 18 Feb 2020 13:08:00 +0100
Subject: [PATCH] spi: spidev: Fix CS polarity if GPIO descriptors are used

Commit f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
amended of_spi_parse_dt() to always set SPI_CS_HIGH for SPI slaves whose
Chip Select is defined by a "cs-gpios" devicetree property.

This change broke userspace applications which issue an SPI_IOC_WR_MODE
ioctl() to an spidev:  Chip Select polarity will be incorrect unless the
application is changed to set SPI_CS_HIGH.  And once changed, it will be
incompatible with kernels not containing the commit.

Fix by setting SPI_CS_HIGH in spidev_ioctl() (under the same conditions
as in of_spi_parse_dt()).

Fixes: f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
Reported-by: Simon Han <z.han-pnUOlEj4XnTQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Lukas Wunner <lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org>
Reviewed-by: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Link: https://lore.kernel.org/r/fca3ba7cdc930cd36854666ceac4fbcf01b89028.1582027457.git.lukas-JFq808J9C/izQB+pC5nmwQ@public.gmane.org
Signed-off-by: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org # v5.1+
---
 drivers/spi/spidev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index 1e217e3e9486..2ab6e782f14c 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -396,6 +396,7 @@ spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		else
 			retval = get_user(tmp, (u32 __user *)arg);
 		if (retval == 0) {
+			struct spi_controller *ctlr = spi->controller;
 			u32	save = spi->mode;
 
 			if (tmp & ~SPI_MODE_MASK) {
@@ -403,6 +404,10 @@ spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 				break;
 			}
 
+			if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
+			    ctlr->cs_gpiods[spi->chip_select])
+				tmp |= SPI_CS_HIGH;
+
 			tmp |= spi->mode & ~SPI_MODE_MASK;
 			spi->mode = (u16)tmp;
 			retval = spi_setup(spi);
-- 
2.20.1