On Tue, Mar 3, 2015 at 6:45 PM, Rojhalat Ibrahim [off-list ref] wrote:

On Thursday 26 February 2015 18:54:53 Alexandre Courbot wrote:

quoted

On Thu, Feb 12, 2015 at 1:28 AM, Rojhalat Ibrahim [off-list ref] wrote:

quoted

Use the new gpiod_get_array and gpiod_put_array functions for obtaining and
disposing of GPIO descriptors.

Cc: David Miller <davem@davemloft.net>
Signed-off-by: Rojhalat Ibrahim <redacted>
---
Change log:
  v5: no change
  v4: use shorter names for members of struct gpio_descs
  v3: no change
  v2: use the new interface

 drivers/net/phy/mdio-mux-gpio.c | 60 ++++++++++++-----------------------------
 1 file changed, 17 insertions(+), 43 deletions(-)

diff --git a/drivers/net/phy/mdio-mux-gpio.c b/drivers/net/phy/mdio-mux-gpio.c
index 320eb15..c49ad09 100644
--- a/drivers/net/phy/mdio-mux-gpio.c
+++ b/drivers/net/phy/mdio-mux-gpio.c

@@ -12,33 +12,30 @@
 #include <linux/module.h>
 #include <linux/phy.h>
 #include <linux/mdio-mux.h>
-#include <linux/of_gpio.h>
+#include <linux/gpio/consumer.h>

 #define DRV_VERSION "1.1"
 #define DRV_DESCRIPTION "GPIO controlled MDIO bus multiplexer driver"

-#define MDIO_MUX_GPIO_MAX_BITS 8
-
 struct mdio_mux_gpio_state {
-       struct gpio_desc *gpio[MDIO_MUX_GPIO_MAX_BITS];
-       unsigned int num_gpios;
+       struct gpio_descs *gpios;
        void *mux_handle;
 };

 static int mdio_mux_gpio_switch_fn(int current_child, int desired_child,
                                   void *data)
 {
-       int values[MDIO_MUX_GPIO_MAX_BITS];
-       unsigned int n;
        struct mdio_mux_gpio_state *s = data;
+       int values[s->gpios->ndescs];
+       unsigned int n;

        if (current_child == desired_child)
                return 0;

-       for (n = 0; n < s->num_gpios; n++) {
+       for (n = 0; n < s->gpios->ndescs; n++)
                values[n] = (desired_child >> n) & 1;
-       }
-       gpiod_set_array_cansleep(s->num_gpios, s->gpio, values);
+
+       gpiod_set_array_cansleep(s->gpios->ndescs, s->gpios->desc, values);

One suggestion for a possible further improvement: it would be great
if the gpiod_set/get_array() functions would work on a struct
gpio_descs so users don't have to pass both the number of GPIOs and
the array.

I don't know whether it would be desirable to keep alternative
functions that preserve the current form, for users who want to set
multiple GPIOs but cannot use gpiod_get_array(). struct gpiod_descs is
easy to build, so maybe we don't need them?

I thought about that, but didn't want to change the interface in this
patch series.

Furthermore there is this use case (my use case):

I acquire a descriptor array for multiple data outputs and (among others) a
single descriptor for a clock output. Afterwards I want to set the data bits
and simultaneously clear the clock bit (using gpiod_set_array) before setting
only the clock output (using gpiod_set_value).

Therefore I need an array containing the data bits and the clock bit which
is easy to build.

I could also create a struct gpiod_descs but it would be more complicated
since I would have to allocate a new struct before populating it with the
descriptors and also free the allocated memory afterwards. It's not really
a big deal but more complicated than before.

But this might not be a very common use case.

If we can assume that for the common use case the group of descriptors that
can be acquired using gpiod_get_array() is the same group that should be
set using gpiod_set_array(), it might make sense to change the interface.

Ah, thanks for sharing your use-case. I wish I had heard it earlier as
it seems we should make things more flexible than they currently are.

If I followed you correctly, you need to call gpiod_get_array() to
obtain the data lines, and gpiod_get() for the clock line. Then you
need to allocate a new array of gpio_desc * and copy all the
descriptors there before calling gpiod_set_array(). So simply put, the
struct gpio_descs you obtained is just useless to you.

It seems like we have been doing things wrong. Maybe gpiod_get_array()
should simply take a pointer to a gpio_desc * array that it would
fill, as you originally proposed?

So now, the question is: do we need struct gpiod_descs at all? It can
help reducing the number of arguments passed to functions, but also
makes the whole API more rigid. Use it with gpiod_get_array(), and you
end up with unneeded copies and memory allocations. Pass it to
gpiod_set_array() and you cannot do things like setting only part of
the GPIOs you requested.

Argh, and looking closer there is some possible confusion between
gpiod_set_array() and gpiod_get_array(). One might expect the latter
to return the *values* of the GPIOs, considering the name of the
former, while it actually is the array counterpart of gpiod_get(). To
be consistent with the single descriptor API, I suppose we should
rename gpiod_set_array() to gpiod_set_array_value(). But that's a
separate issue.

For now, since you are the main user of the array API, what is your
opinion about gpiod_descs? Do you think it is worth making the API
less flexible just to not have to carry an array lengh separately?
Should we just get rid of it?