linux-kernel - Re: [PATCH V2] spmi: pmic-arb: Enforce the ownership check optionally

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Date:   Thu, 31 Aug 2017 16:37:29 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     Kiran Gunda <kgunda@...eaurora.org>, gregkh@...uxfoundation.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Abhijeet Dharmapurikar <adharmap@...eaurora.org>,
        David Collins <collinsd@...eaurora.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH V2] spmi: pmic-arb: Enforce the ownership check optionally

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.

Shawn