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Message-ID: <CAAVeFuJigwAg09p4LQ+9g_LYusYe_G-y_aBWP0rr-AG-yz5V-A@mail.gmail.com> Date: Tue, 22 Jul 2014 13:30:59 +0900 From: Alexandre Courbot <gnurou@...il.com> To: Guenter Roeck <linux@...ck-us.net> 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 Thu, Jul 17, 2014 at 11:34 PM, Guenter Roeck <linux@...ck-us.net> wrote: > 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 is correct. The reason is to have a separate authority to assigns GPIOs and prevent drivers from arbitrarily requesting any GPIO they want, as long as everybody sticks to the gpiod interface. > 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. If you want to benefit from the active-low property but cannot use gpiod_get() for some reason, you can still request a GPIO by gpio_request_one() and then convert it to a descriptor with gpio_to_desc(), which is what I suspect your patch will allow you to do. But the real fix would be to work any limitations that gpiod has that prevent you from doing what you need. I am not familiar with mdio-gpio - could you explain what makes it impossible to convert this driver to the new model in your view? -- 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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