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Message-ID: <53C7DEE3.6060107@roeck-us.net> Date: Thu, 17 Jul 2014 07:34:11 -0700 From: Guenter Roeck <linux@...ck-us.net> To: Alexandre Courbot <gnurou@...il.com> CC: "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linus Walleij <linus.walleij@...aro.org> Subject: Re: [PATCH] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request_one On 07/17/2014 12:26 AM, Alexandre Courbot wrote: > On Thu, Jul 17, 2014 at 3:37 PM, Guenter Roeck <linux@...ck-us.net> wrote: >> On 07/16/2014 11:09 PM, Alexandre Courbot wrote: >>> >>> On Thu, Jul 17, 2014 at 8:11 AM, Guenter Roeck <linux@...ck-us.net> wrote: >>>> >>>> The gpio include file and the gpio documentation declare and document >>>> GPIOF_ACTIVE_LOW as one of the flags to be passed to gpio_request_one >>>> and related functions. However, the flag is not evaluated or used. >>>> >>>> Check the flag in gpio_request_one and set the gpio internal flag >>>> FLAG_ACTIVE_LOW if it is set. >>> >>> >>> What is the point since the integer GPIO API has no clue of the >>> active-low status of a GPIO? It is only used by the gpiod and sysfs >>> interfaces. >>> >> >> One can use gpio_request_one() to export a gpio pin to user space from >> the kernel. That code path does use the flag, as you point out yourself >> above. > > Ok, in that case I suppose it makes sense. > > Reviewed-by: Alexandre Courbot <acourbot@...dia.com> > >> One could also argue that the integer gpio API _should_ support this as >> well, >> but that is a different question. > > Probably not going to happen. The integer GPIO interface is deprecated > and users who need new features should seriously consider switching to > gpiod. > The new API is unfortunately not equivalent to the old one. For example, if I understand correctly, gpiod_get is expected to be used instead of gpio_request_one. That may work nicely in a world with full DT or ACPI support, but doesn't work as well otherwise unless one drops the notion of using platform specific drivers built as modules (gpiod_add_lookup_table is not exported, and there is no remove function). Specifically, I don't see an easy way to convert mdio-gpio to use the new model, and that driver could really use support for an API which supports active-low pins. And even if gpiod_add_lookup_table was supported, converting a driver like this would be a major pain. Sure, it would be all easy if there would be a gpiod equivalent to gpio_request_one and gpio_request_array, but that is not the case. This makes converting drivers from the old to the new model challenging enough that I suspect that it won't really happen. Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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