Messages in this thread | | | Date | Wed, 16 Dec 2015 10:11:46 +0000 | From | Martyn Welch <> | Subject | Re: [PATCH 2/3] Add support for monitoring gpio switches |
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On 11/12/15 09:08, Linus Walleij wrote: > On Fri, Dec 4, 2015 at 6:31 PM, Martyn Welch > <martyn.welch@collabora.co.uk> wrote: > >> Select Chromebooks have gpio attached to switches used to cause the >> firmware to enter alternative modes of operation and/or control other >> device characteristics (such as write protection on flash devices). This >> patch adds a driver that exposes a read-only interface to allow these >> signals to be read from user space. >> >> This functionality has been generalised to provide support for any device >> with device tree support which needs to identify a gpio as being used for a >> specific task. >> >> Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk> > > If you want to do this thing, also propose a device tree binding document > for "gpio-switch". > > But first (from Documentation/gpio/drivers-on-gpio.txt): > > - gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line > can generate interrupts in response to a key press. Also supports debounce. >
This one generates input events from gpio. I'm not looking to generate events.
> - gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your > GPIO line cannot generate interrupts, so it needs to be periodically polled > by a timer. >
Ditto (but using a polled mechanism rather than interrupts)
> - extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an > external connector status, such as a headset line for an audio driver or an > HDMI connector. It will provide a better userspace sysfs interface than GPIO. >
This appears to be exclusively for monitoring insertion events, or am I missing something?
> So you mean none of these apply for this case? >
No, I'm looking for a mechanism to identify GPIO as connected to a specific signal, which is provided across multiple devices, but which might be implemented subtly differently on different platforms (i.e. active high/low) and on different GPIO lines.
> Second: what you want to do is export a number of GPIOs with certain names > to userspace. This is something very generic and should be implemented > as such, not as something Chromebook-specific. >
I'd agree that my first implementation was ChromeBook specific, but I'm fairly sure that my last attempt wasn't. I've mentioned ChromeBooks as an example of an existing use case.
> Patches like that has however already been suggested, and I have NACKed > them because the GPIO sysfs ABI is insane, and that is why I am refactoring > the world to create a proper chardev ABI for GPIO instead. See: > http://marc.info/?l=linux-gpio&m=144550276512673&w=2 >
I can certainly understand the rationale for the changes that you are proposing, though do worry that it does make it a bit tougher to use from scripting languages. I see that the question of how to provide functionality equivalent to the above was raised and no answer was forthcoming. Is there a plan for supporting the identification of a GPIO line serving a specific purpose?
What is the status of the mentioned patch series?
Martyn
> So for the moment, NACK on this, please participate in creating the > *right* ABI for GPIO instead of trying to shoehorn stuff into the dying > sysfs ABI. > > Yours, > Linus Walleij >
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