Hello Geert,

On Fri, Mar 03, 2017 at 08:21:05PM +0100, Geert Uytterhoeven wrote:

quoted

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 91e7dddbf72c..2f4cdd4e7b4f 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c

@@ -3022,7 +3022,7 @@ static int sci_probe_single(struct platform_device *dev,
                return ret;

        sciport->gpios = mctrl_gpio_init(&sciport->port, 0);
-       if (IS_ERR(sciport->gpios) && PTR_ERR(sciport->gpios) != -ENOSYS)
+       if (IS_ERR(sciport->gpios))
                return PTR_ERR(sciport->gpios);

Now the sh-sci driver fails to probe on legacy platforms where GPIOLIB=n.
The check for -ENOSYS made it succeed before.

That's right, intended and the only option that's save (for some
definition of save; the obvious downside is that there is no
/dev/tty$whatever for you).

Ignoring -ENOSYS is only ok if your device doesn't have a cts-gpio. If
it has, ignoring -ENOSYS hides bugs because the driver sends data while
it shouldn't or cannot signal the other side that it should stop (or
start) a transmission.

So the options are:
 - enable GPIOLIB (maybe enforce that by letting the driver select it)
 - introduce a CONFIG_HALFGPIOLIB that makes gpiod_get_optional and
   mctrl_gpio_init return only then -ENOSYS if there is a gpio specified
   and NULL otherwise.

quoted

Then mctrl_gpio_to_gpiod isn't called. I don't have a machine to test
this, but I think currently this makes the machine barf to continue
here because with sciport->gpios = ERR_PTR(-ENOSYS) calling

        mctrl_gpio_to_gpiod(sciport->gpios, ...)

is a bad idea.

If sciport->gpios == ERR_PTR(-ENOSYS), CONFIG_GPIOLIB is not enabled, the
feature is not available, and mctrl_gpio_to_gpiod() will not
dereference the error
pointer.

Ah, makes sense.

quoted

quoted

Perhaps mctrl_gpio_to_gpiod() should always return NULL if !CONFIG_GPIOLIB?

No, mctrl_gpio_to_gpiod is right. You are only supposed to call it if
mctrl_gpio_init succeeded.

Then I have to add checks for sciport->gpios == ERR_PTR(-ENOSYS)...

No, ignoring -ENOSYS is wrong.

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-K?nig            |
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