Re: [PATCH] gpio: gpio-mockup: Fix usage of new GPIO_LINE_DIRECTION

[Kent Gibson <warthog618@xxxxxxxxx>]

On Tue, Dec 10, 2019 at 10:55:15PM +0800, Kent Gibson wrote:
> On Tue, Dec 10, 2019 at 03:11:12PM +0100, Bartosz Golaszewski wrote:
> > wt., 10 gru 2019 o 03:15 Kent Gibson <warthog618@xxxxxxxxx> napisał(a):
> > >
> > > Restore the external behavior of gpio-mockup to what it was prior to the
> > > change to using GPIO_LINE_DIRECTION.
> > >
> > > Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
> > > ---
> > >
> > > Fix a regression introduced in v5.5-rc1.
> > >
> > > The change to GPIO_LINE_DIRECTION reversed the polarity of the
> > > dir field within gpio-mockup.c, but overlooked inverting the value on
> > > initialization and when returned by gpio_mockup_get_direction.
> > > The latter is a bug.
> > > The former is a problem for tests which assume initial conditions,
> > > specifically the mockup used to initialize chips with all lines as inputs.
> > > That superficially appeared to be the case after the previous patch due
> > > to the bug in gpio_mockup_get_direction.
> > >
> > >  drivers/gpio/gpio-mockup.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpio/gpio-mockup.c b/drivers/gpio/gpio-mockup.c
> > > index 56d647a30e3e..c4fdc192ea4e 100644
> > > --- a/drivers/gpio/gpio-mockup.c
> > > +++ b/drivers/gpio/gpio-mockup.c
> > > @@ -226,7 +226,7 @@ static int gpio_mockup_get_direction(struct gpio_chip *gc, unsigned int offset)
> > >         int direction;
> > >
> > >         mutex_lock(&chip->lock);
> > > -       direction = !chip->lines[offset].dir;
> > > +       direction = chip->lines[offset].dir;
> > >         mutex_unlock(&chip->lock);
> > >
> > >         return direction;
> > > @@ -395,7 +395,7 @@ static int gpio_mockup_probe(struct platform_device *pdev)
> > >         struct gpio_chip *gc;
> > >         struct device *dev;
> > >         const char *name;
> > > -       int rv, base;
> > > +       int rv, base, i;
> > >         u16 ngpio;
> > >
> > >         dev = &pdev->dev;
> > > @@ -447,6 +447,9 @@ static int gpio_mockup_probe(struct platform_device *pdev)
> > >         if (!chip->lines)
> > >                 return -ENOMEM;
> > >
> > > +       for (i = 0; i < gc->ngpio; i++)
> > > +               chip->lines[i].dir = GPIO_LINE_DIRECTION_IN;
> > > +
> > >         if (device_property_read_bool(dev, "named-gpio-lines")) {
> > >                 rv = gpio_mockup_name_lines(dev, chip);
> > >                 if (rv)
> > > --
> > > 2.24.0
> > >
> > 
> > Hi Kent,
> > 
> > I was applying and testing your libgpiod series and noticed that the
> > gpio-tools tests fail after applying patches 16 & 17 (with linux
> > v5.5-rc1). Is this fix related to this?
> > 
> 
> I don't think so.  I've only been able to trip this problem with a
> couple of corner cases in my Go uapi test suite.
> I have been unable to reproduce it with the tools as it requires
> multiple requests with the same chip fd, including an as-is, to trip.
> 

It turns out that I can reproduce the bug with my gpiod tools:

root@firefly:/home/kent/gpiod/cmd/gpiodctl# uname -a
Linux firefly 5.5.0-rc1 #23 SMP Mon Dec 9 16:26:33 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
root@firefly:/home/kent/gpiod/cmd/gpiodctl# modprobe gpio-mockup gpio_mockup_ranges=-1,4
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl get gpiochip0 1
0
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl info
gpiochip0 - 4 lines:
	line   0:     unnamed      unused   input  active-high
	line   1:     unnamed      unused   input  active-high
	line   2:     unnamed      unused   input  active-high
	line   3:     unnamed      unused   input  active-high
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl get --as-is gpiochip0 1
0
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl info
gpiochip0 - 4 lines:
	line   0:     unnamed      unused   input  active-high
	line   1:     unnamed      unused  output  active-high
	line   2:     unnamed      unused   input  active-high
	line   3:     unnamed      unused   input  active-high

Note that the line 1 direction has flipped for no reason.

With the patched kernel that doesn't happen:

root@firefly:/home/kent/gpiod/cmd/gpiodctl# uname -a
Linux firefly 5.5.0-rc1+ #27 SMP Tue Dec 10 01:07:59 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
root@firefly:/home/kent/gpiod/cmd/gpiodctl# modprobe gpio-mockup gpio_mockup_ranges=-1,4
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl get gpiochip0 1
0
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl info
gpiochip0 - 4 lines:
	line   0:     unnamed      unused   input  active-high
	line   1:     unnamed      unused   input  active-high
	line   2:     unnamed      unused   input  active-high
	line   3:     unnamed      unused   input  active-high
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl get --as-is gpiochip0 1
0
root@firefly:/home/kent/gpiod/cmd/gpiodctl# ./gpiodctl info
gpiochip0 - 4 lines:
	line   0:     unnamed      unused   input  active-high
	line   1:     unnamed      unused   input  active-high
	line   2:     unnamed      unused   input  active-high
	line   3:     unnamed      unused   input  active-high


I would prefer to demonstrate this with the libgpiod tools, but they
don't support as-is on gets.  I recall suggesting adding it and you
asking why - who would need it.  This is a concrete example of my
response at the time - so you can exercise the full API for testing.

Cheers,
Kent.