Re: [PATCH] pinctrl: cherryview: Add quirk with custom translation of ACPI GPIO numbers

[Brian Norris]

Hi Mika,

I'm following along with attempts to "fix" our user space to paper over
this issue, and I think some of this conversation missed the mark.
(Sorry for jumping in late.)

On Tue, Mar 10, 2020 at 04:49:13PM +0200, Mika Westerberg wrote:
> On Tue, Mar 10, 2020 at 03:12:00PM +0100, MichaÅ Stanek wrote:
> > On Mon, Feb 10, 2020 at 11:14 AM Mika Westerberg
> > <mika.westerberg@xxxxxxxxxxxxxxx> wrote:
> > > On Sat, Feb 08, 2020 at 07:43:24PM +0100, MichaÅ Stanek wrote:
> > > > > >
> > > > > > Hi Mika,
> > > > > >
> > > > > > The previous patches from Dmitry handled IRQ numbering, here we have a
> > > > > > similar issue with GPIO to pin translation - hardcoded values in FW
> > > > > > which do not agree with the (non-consecutive) numbering in newer
> > > > > > kernels.
> > > > >
> > > > > Hmm, so instead of passing GpioIo/GpioInt resources to devices the
> > > > > firmware uses some hard-coded Linux GPIO numbering scheme? Would you
> > > > > able to share the exact firmware description where this happens?
> > > >
> > > > Actually it is a GPIO offset in ACPI tables for Braswell that was
> > > > hardcoded in the old firmware to match the previous (consecutive)
> > > > Linux GPIO numbering.
> > >
> > > Can you share the ACPI tables and point me to the GPIO that is using
> > > Linux number?
> > 
> > I think this is the one:
> > https://chromium-review.googlesource.com/c/chromiumos/third_party/coreboot/%2B/286534/2/src/mainboard/google/cyan/acpi/chromeos.asl
> > 
> > On Kefka the sysfs GPIO number for wpsw_cur was gpio392 before the
> > translation change occurred in Linux.
> 
> But that table does not seem to have any GPIO numbers in it.

Actually, it's encoding pin numbers, not GPIO numbers. The 0x10016 (or
now, 0x10013) is encoding a bank offset (0x10000) and pin number (0x16
or 0x13). The actual pin numbers is 0x16, I believe, but someone decided
to subtract 3, because the Linux numbering used to be contiguous,
skipping over the hole between 11 and 15.

So no, nobody was hard-coding gpiochip numbers -- we were hard-coding
the contiguous pin number (relative to the bank). Now that commit
03c4749dd6c7ff94 ("gpio / ACPI: Drop unnecessary ACPI GPIO to Linux GPIO
translation") made those non-contiguous, we're kinda screwed -- we have
to guess (based on the kernel version number) whether pin numbers
(within a single bank!) are contiguous or not.

> > > This is something that should be fixed in userspace. Using global Linux
> > > GPIO or IRQ numbers is fragile and source of issues like this.

To be clear, we're not hard-coding global <anything> numbers in user
space.

> > > in case of sysfs, you can
> > > find the base of the chip

We're doing that.

> > > and then user relative numbering against it or
> > > switch

^^ This is the problem. The *bank-relative* numbers changed.

> > > Both cases the GPIO number are relative against the GPIO chip so
> > > they work even if global Linux GPIO numbering changes.
> > 
> > I analyzed crossystem source code and it looks like it is doing
> > exactly what you're saying without any hardcoded assumptions.

^^ Exactly.

> > With the newer kernel the gpiochip%d number is different so crossystem
> > ends up reading the wrong pin.
> 
> Hmm, so gpiochipX is also not considered a stable number. It is based on
> ARCH_NR_GPIOS which may change. So if the userspace is relaying certain GPIO
> chip is always gpichip200 for example then it is wrong.

If you just read the last sentence from Michal, you get the wrong
picture. There's no hard-coding of gpiochipX numbers going on. We only
had the pin offsets "hardcoded" (in ACPI), and the kernel driver
unilaterally changed from a contiguous mapping to a non-contiguous
mapping.

How do you recommend determining (both pre- and
post-commit-03c4749dd6c7ff94) whether pin 22 is at offset 22, vs. offset
19?

Brian