Re: [PATCH] pinctrl: qcom: qdf2xxx: expose only some GPIO pins

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Fri 23 Jun 05:33 PDT 2017, Linus Walleij wrote:

> On Thu, Jun 22, 2017 at 10:54 PM, Timur Tabi <timur@codeaurora.org> wrote:
> 
> > On Qualcomm Technologies QDF2xxx platforms, only a subset of the GPIOs
> > are actually available to the HLOS.  The others are blocked by the XPU,
> > and any attempt to access them will cause an XPU violation that halts
> > the system.
> 
> That's a bummer. Looking for Björn's review on this patch.
> 

The TLMM block on this platform has N gpios, regardless of the XPU
configuration. The ACPI table provides the kernel with a list of
available "logical" GPIOs based on some system specification (or
reference design perhaps?).

I have not seen the Qualcomm server platforms, but I imagine that
customers can alter this list.


I think the numbering of the GPIOs should be that of the TLMM and the
"logical" names should be populated from ACPI by using gpio_chip->names.

The question left is how to represent the XPU locked gpios - a problem
we do share with in the mobile TLMM drivers.


It seems that if we extend the msm_pingroup with a flag to carry the XPU
lock information and then implement pinmux_ops->request() and deny any
requests on the locked pins, we should cover all[*] the normal GPIO code
paths.

[*] Except the reported case of gpiochip_add_data() looping over all
pins and calling get_direction() without first requesting the pin.

@Linus, do you see any flaws in this scheme?


PS. gpiochip_generic_request() ends up calling pinmux_ops->request()

Regards,
Bjorn