Re: [PATCH v2 3/8] pinctrl: msm: Add ability for drivers to supply a reserved GPIO list

[Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>]

On Fri 07 Jun 04:10 PDT 2019, Ard Biesheuvel wrote:

> On Fri, 7 Jun 2019 at 10:29, Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> >
> > When booting MSM based platforms with Device Tree or some ACPI
> > implementations, it is possible to provide a list of reserved pins
> > via the 'gpio-reserved-ranges' and 'gpios' properties respectively.
> > However some ACPI tables are not populated with this information,
> > thus it has to come from a knowledgable device driver instead.
> >
> > Here we provide the MSM common driver with additional support to
> > parse this informtion and correctly populate the widely used
> > 'valid_mask'.
> >
> > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> 
> I'm not sure if this is the correct approach. Presumably, on ACPI
> systems, all the pinctl stuff is already set up by the firmware, and
> so we shouldn't touch *any* pins unless they have been requested
> explicitly. Is there any way we can support this in the current
> framework?
> 

The only reason why we do this (at least the initial reason) is because
gpiolib will read the current state of all GPIOs during initialization.

But due to the sensitive nature of the application using these pins
Linux is prohibited from touching the associated GPIO/pinmux/pinconf
registers - resulting in a security violation if we allow gpiolib to
touch them.


When it comes to pinmux/pinconf those are only poked explicitly and
those seems to be described in PEP nodes, such as:

	Package (0x02)
	{
	    "TLMMGPIO",
	    Package (0x06)
	    {
		0x2C,
		One,
		Zero,
		One,
		Zero,
		Zero
	    }
	},

So the pinctrl-sdm845/msm drivers gives us GPIOs, but for pinconf and
pinmux there's a need for something very different from what we're used
to.

Regards,
Bjorn

> > ---
> >  drivers/pinctrl/qcom/pinctrl-msm.c | 18 ++++++++++++++++++
> >  drivers/pinctrl/qcom/pinctrl-msm.h |  1 +
> >  2 files changed, 19 insertions(+)
> >
> > diff --git a/drivers/pinctrl/qcom/pinctrl-msm.c b/drivers/pinctrl/qcom/pinctrl-msm.c
> > index ee8119879c4c..3ac740b36508 100644
> > --- a/drivers/pinctrl/qcom/pinctrl-msm.c
> > +++ b/drivers/pinctrl/qcom/pinctrl-msm.c
> > @@ -607,8 +607,23 @@ static int msm_gpio_init_valid_mask(struct gpio_chip *chip)
> >         int ret;
> >         unsigned int len, i;
> >         unsigned int max_gpios = pctrl->soc->ngpios;
> > +       const int *reserved = pctrl->soc->reserved_gpios;
> >         u16 *tmp;
> >
> > +       /* Driver provided reserved list overrides DT and ACPI */
> > +       if (reserved) {
> > +               bitmap_fill(chip->valid_mask, max_gpios);
> > +               for (i = 0; reserved[i] >= 0; i++) {
> > +                       if (i >= max_gpios || reserved[i] >= max_gpios) {
> > +                               dev_err(pctrl->dev, "invalid list of reserved GPIOs\n");
> > +                               return -EINVAL;
> > +                       }
> > +                       clear_bit(reserved[i], chip->valid_mask);
> > +               }
> > +
> > +               return 0;
> > +       }
> > +
> >         /* The number of GPIOs in the ACPI tables */
> >         len = ret = device_property_read_u16_array(pctrl->dev, "gpios", NULL,
> >                                                    0);
> > @@ -964,6 +979,9 @@ static void msm_gpio_irq_handler(struct irq_desc *desc)
> >
> >  static bool msm_gpio_needs_valid_mask(struct msm_pinctrl *pctrl)
> >  {
> > +       if (pctrl->soc->reserved_gpios)
> > +               return true;
> > +
> >         return device_property_read_u16_array(pctrl->dev, "gpios", NULL, 0) > 0;
> >  }
> >
> > diff --git a/drivers/pinctrl/qcom/pinctrl-msm.h b/drivers/pinctrl/qcom/pinctrl-msm.h
> > index c12048e54a6f..23b93ae92269 100644
> > --- a/drivers/pinctrl/qcom/pinctrl-msm.h
> > +++ b/drivers/pinctrl/qcom/pinctrl-msm.h
> > @@ -121,6 +121,7 @@ struct msm_pinctrl_soc_data {
> >         bool pull_no_keeper;
> >         const char *const *tiles;
> >         unsigned int ntiles;
> > +       const int *reserved_gpios;
> >  };
> >
> >  extern const struct dev_pm_ops msm_pinctrl_dev_pm_ops;
> > --
> > 2.17.1
> >
> >
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