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SubjectRe: [PATCH V2] spmi: pmic-arb: Enforce the ownership check optionally
On Thu, Aug 31, 2017 at 06:30:48PM -0700, Stephen Boyd wrote:
> On 08/31, Shawn Guo wrote:
> > On Wed, Aug 30, 2017 at 02:02:03PM -0700, Stephen Boyd wrote:
> > > On 08/26, Shawn Guo wrote:
> > > > On Fri, Aug 25, 2017 at 04:18:18PM -0700, Stephen Boyd wrote:
> > > > >
> > > > > Right. Does the GPIO work? If so, it sounds like the read/write
> > > > > access checks in spmi pmic arb don't work properly.
> > > >
> > > > The check works. With the check in there, PM8916 GPIO doesn't work.
> > > > However, the consequence is that not only user3 but all GPIO leds under
> > > > 'leds' node will fail to register, because any GPIO led's failing on
> > > > create_gpio_led() makes leds-gpio driver probe fail as a while. That's
> > > > how leds-gpio driver works.
> > > >
> > > > Also, per schematics, PM8916 GPIO1 is indeed routed to user3 LED on
> > > > db410c board. Why do you think apq8016-sbc device tree shouldn't use
> > > > the GPIO for that at all? Isn't it firmware's fault that the ownership
> > > > of the peripheral is not properly configured?
> > >
> > > If the ownership was not properly configured in the firmware,
> > > then I imagine it would mean that we can't control the GPIO for
> > > the LED. But that doesn't seem to be true. I can see on my board
> > > that I get impermissible write failures on the GPIO when
> > > controlling the GPIO brightness, but it doesn't actually matter
> > > because the led still lights up. So the checks for write/read
> > > permission seem incorrect, or they're not being enforced.
> >
> > I'm not sure what is happening on your side. As I said above, with the
> > 4.13-rc series, leds-gpio driver doesn't probe at all, due to the
> > impermissible write to PM8916 GPIO in function create_gpio_led(), and
> > none of the LEDs lights up on my board.
> >
>
> Yep. I understand all that.
>
> Sorry, I forgot to mention I modified the SPMI PMIC arb code on
> v4.13-rc7 to continue even though a permission fault may happen
> by deleting the 'return -EPERM' lines. So the LED GPIO driver is
> still probing for me, and I see that the GPIOs work regardless of
> any permission problems that may have been enforced in the
> hardware. I thought the permission checks that the software is
> looking at to return EPERM were enforced in hardware, but that
> doesn't seem to be the case. That's all I was wondering about.

Ah, okay. You were asking about the check in hardware, while I was
talking about the check in software. Yes, now we are on the same page:
the permission check in hardware seems not enforced. That's why LED
works after we merely remove the check in SPMI PMIC arb driver code.

Shawn

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