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SubjectRe: Re: [PATCH] pinctrl: intel: Implements gpio free function
On Thu, Mar 21, 2019 at 08:22:40PM +0800, zhuchangchun@cvte.com wrote:
> On Thu, Mar 21, 2019 at 07:20:56PM +0800, zhuchangchun@cvte.com wrote:
> > After you unexport GPIO it can go back to any previous mode it
> was. If
> > you need to use it as GPIO then why unexport it in the first
> place?
> > --> because we need use the GPIO for device reset, we want to
> recover
> > the GPIO value after reset done.If we don't unexport it, then
> reboot
> > the
> > intel SOC(not power off), the GPIO's value will stay until the
> GPIO be
> > reinit.
> > I tested the GPIO signal with oscilloscope, if power off the SOC,
> > then
> > power on, the GPIO value can recover its original value. This will
> > infruence
> > the peripheral device working condition.
>
> If I understand correctly you have some peripheral connected to Intel
> based board and one GPIO is used to reset the peripheral.
>
> You say it works fine if you power cycle the board but it does not when
> you issue 'reboot' command. Did I understood the problem correctly?
>
> --> Yes , so I add the -> free callback, it fixes the problem.

OK, so you then write 1 to the sysfs to assert reset, right? And in your
patch you change the mode to input effectively deasserting the reset.

Why not simply do following instead of unexport?

# echo 0 > /sys/class/gpio/gpioXX/value

or even

# echo 0 > /sys/class/gpio/gpioXX/value
# echo in > /sys/class/gpio/gpioXX/direction

Am I missing something?

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