[Question] How to implement GPIO driver for sparse hw numbers?

[Question] How to implement GPIO driver for sparse hw numbers?

[Masahiro Yamada]

Hi GPIO experts,


I am trying to implement a new GPIO driver for a new SoC.

I'd like to consult experts how to solve my problem.

According to the hardware specification book,
the GPIO ports on my SoC are labelled from PORT0 to PORT307 as follows:

 PORT0,   PORT1,   PORT2,       PORT7,    --> register offset 0x0
 PORT10,  PORT11,  PORT12, ..., PORT17    --> register offset 0x8
 PORT20,  PORT21,  PORT22, ..., PORT27,   --> register offset 0x10
       ...
 PORT290, PORT291, PORT292, ... PORT297   --> register offset 0xe8
 PORT300, PORT301, PORT302, ... PORT307   --> register offset 0x90


Unfortunately, the port numbers are not contiguous.
The port numbers with 8 or 9 in the one's place
(such as PORT8, PORT9, PORT18, PORT19, ...) are missing.


In my understanding, the GPIO driver framework requires that
the hw numbers should be contiguous within each GPIO chip.

If I try to follow this rule, the hwnum given to GPIOLIB functions
does not correspond to the port documented in the hardware specification.

  gpiochip_get_desc(chip, 0);   /* get descripter of PORT0 */
  gpiochip_get_desc(chip, 1);   /* get descripter of PORT1 */
        ...
  gpiochip_get_desc(chip, 7);   /* get descripter of PORT7 */
  gpiochip_get_desc(chip, 8);   /* get descripter of PORT10 */  /* confusing! */
  gpiochip_get_desc(chip, 9);   /* get descripter of PORT11 */  /* confusing! */
  gpiochip_get_desc(chip, 10);   /* get descripter of PORT12 */  /*
confusing! */
        ...


One solution I have come up with is to divide the GPIO chip into 31 banks,
with 8 ports in each.
But, I hesitate to describe 31 nodes in my device tree.

   port0x : gpio@55000000 {
             compatible = ...
             reg = <0x55000000 0x8>;
   };

   port1x : gpio@55000008 {
             compatible = ...
             reg = <0x55000008 0x8>;
   };

          ...

   port29x : gpio@5500008c {
             compatible = ...
             reg = <0x5500008c 0x8>;
   };

   port30x : gpio@55000090 {
             compatible = ...
             reg = <0x55000090 0x8>;
   };


Any good ideas?

Thanks,



-- 
Best Regards
Masahiro Yamada

Re: [Question] How to implement GPIO driver for sparse hw numbers?

[Linus Walleij]

On Fri, Jun 19, 2015 at 5:27 AM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:

> In my understanding, the GPIO driver framework requires that
> the hw numbers should be contiguous within each GPIO chip.

Yes but noone says that .request() to the driver has to succeed
on every GPIO so just cover all GPIOs from 0 to 307 with
your GPIO chip and then implement your "holes" in the GPIO
range from 0 to 307 by letting .request() fail.

Yours,
Linus Walleij

Re: [Question] How to implement GPIO driver for sparse hw numbers?

[Masahiro Yamada]

Hi Linus,


2015-07-15 7:04 GMT+09:00 Linus Walleij <linus.walleij@linaro.org>:
> On Fri, Jun 19, 2015 at 5:27 AM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>
>> In my understanding, the GPIO driver framework requires that
>> the hw numbers should be contiguous within each GPIO chip.
>
> Yes but noone says that .request() to the driver has to succeed
> on every GPIO so just cover all GPIOs from 0 to 307 with
> your GPIO chip and then implement your "holes" in the GPIO
> range from 0 to 307 by letting .request() fail.

Thanks,
At first I also thought about it, but finally I did not adopt it.

Having holes in the GPIO range is not handy because:

[1] When we map a gpio range into a pin range,
    we must divide "gpio-ranges" property into many lines
       gpio-ranges = <phandle  0    x      8
                      phandle  10   (x+8)  8
                      phandle  20   (x+16) 8
                      phandle  30   (x+24) 8
                              ...

[2] implementation of .set_multiple() gets more complicated




-- 
Best Regards
Masahiro Yamada