Re: [PATCH RFC 2/6 v3] gpio: Add sysfs support to block GPIO API

[Roland Stigge <stigge@antcom.de>]

On 15/10/12 22:30, Linus Walleij wrote:
> I don't like it either, basically because the GPIO sysfs is not
> entirely sound.
> 
> Another patch that is circulating concerns edge triggers and similar,
> and it appear that some parts of the GPIO sysfs is for example
> redefining and exporting IRQchip properties like trigger edge
> in sysfs, while the settings of the irqchip actually used by the driver
> is not reflected in the other direction. So you can *set* these things
> by writing in the GPIO sysfs, but never trust what you *read* from
> there. And you can set what edges an IRQ will trigger on a certain
> GPIO, and the way to handle the IRQs from usespace is to poll
> on a value. This is not really documented but well ...

I'm not convinced this generally also applies to the block GPIO patches.
Or that it can't be fixed.

> The reason an ioctl() IMO is better suited to do the job is that
> it can properly represent a multiple-value operation on several
> GPIOs at the same time in a struct, and it can conversely inform
> userspace about which GPIOs may be a block of signals that
> can be fired simultaneously instead of going to string parsing
> and binary values in sysfs which look like worse hacks to me.

There is no binary values in the sysfs for the block GPIO patches, and
regarding string parsing - yes, that's sysfs. :-)

Roland