Re: [PATCH 1/1] arm64: dts: qcom: msm8994: Reserve gpio ranges

[Petr Vorel <petr.vorel@gmail.com>]

> On Tue, Apr 6, 2021 at 12:52 AM Bjorn Andersson
> <bjorn.andersson@linaro.org> wrote:
> > On Mon 05 Apr 15:02 CDT 2021, Petr Vorel wrote:

> > > Simple testing with /sys/class/gpio/export showed that 85-88.
> > > 3 disables UART. I expect 0-2 are also reserved as on other msm8998.


> > Are you saying that once you export these gpios the uart stops working?

> That might be a Fixes: but certainly not a regression.

> Using GPIO sysfs access is dangerous and if someone enables it into
> their kernel (which requires setting CONFIG_EXPERT) they are
> certainly aware that they are taking a risk. (Same goes for using
> the character device from userspace.)

Not sure if we understand each other. You might think I export GPIO from
userspace on mainline kernel or use CONFIG_EXPERT. None of these is true.

The real problem is that mainline kernel compiled with defconfig resets really
early, thus v2 of this patch [2] is needed.

I just exported GPIO on *downstream* kernel to observe the behaviour.
It was just a simple way for me to find GPIOs which cause reset.
(having docs would be great)

And there is similar reset much later but still before reaching initramfs
in loop_init since a99163e9e708 (during loop_add() on lo->lo_number: 3). And
if I disable CONFIG_BLK_DEV_LOOP, it resets right after reaching initramfs.
I guess that's another problem with DT, but haven't got much further.
But that's a separate problem, gpio-reserved-ranges = <85 4> on tlmm [2]
is still some improvement.

Kind regards,
Petr

[2] https://lore.kernel.org/linux-arm-msm/20210406202936.22500-1-petr.vorel

> Yours,
> Linus Walleij