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

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Date:	Thu, 16 Jul 2015 13:07:20 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Question] How to implement GPIO driver for sparse hw numbers?

Hi Linus,


2015-07-15 7:04 GMT+09:00 Linus Walleij <linus.walleij@...aro.org>:
> On Fri, Jun 19, 2015 at 5:27 AM, Masahiro Yamada
> <yamada.masahiro@...ionext.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
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