Date:   Sun, 12 Aug 2018 14:04:49 +0100
From:   Craig Tatlor <ctatlor97@...il.com>
To:     Christian Lamparter <chunkeey@...il.com>
CC:     linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pinctrl: qcom: Add sdm660 pinctrl driver



On 12 August 2018 13:42:27 BST, Christian Lamparter <chunkeey@...il.com> wrote:
>On Sunday, August 12, 2018 9:18:19 AM CEST you wrote:
>> On 11 August 2018 18:27:43 BST, Christian Lamparter
><chunkeey@...il.com> wrote:
>> >On Saturday, August 11, 2018 6:25:19 PM CEST Craig Tatlor wrote:
>> >> Add initial pinctrl driver to support pin configuration with
>> >> pinctrl framework for sdm660.
>> >> Based off CAF implementation.
>> >> 
>> >> Signed-off-by: Craig Tatlor <ctatlor97@...il.com>
>> >> ---
>> >> 
>> >> diff --git
>> >a/Documentation/devicetree/bindings/pinctrl/qcom,sdm660-pinctrl.txt
>> >b/Documentation/devicetree/bindings/pinctrl/qcom,sdm660-pinctrl.txt
>> >> new file mode 100644
>> >> index 000000000000..85e6c6c17c04
>> >> --- /dev/null
>> >> +++
>> >b/Documentation/devicetree/bindings/pinctrl/qcom,sdm660-pinctrl.txt
>> >> @@ -0,0 +1,195 @@
>> >> +Qualcomm Technologies, Inc. SDM660 TLMM block
>> >> +
>> >> +This binding describes the Top Level Mode Multiplexer block found
>in
>> >the
>> >> +SDM660 platform.
>> >> +
>> >> +- compatible:
>> >> +	Usage: required
>> >> +	Value type: <string>
>> >> +	Definition: must be "qcom,sdm660-pinctrl"
>> >> +
>> >> +- reg:
>> >> +	Usage: required
>> >> +	Value type: <prop-encoded-array>
>> >> +	Definition: the base address and size of the TLMM register
>space.
>> >> +
>> >> +- interrupts:
>> >> +	Usage: required
>> >> +	Value type: <prop-encoded-array>
>> >> +	Definition: should specify the TLMM summary IRQ.
>> >> +
>> >> +- interrupt-controller:
>> >> +	Usage: required
>> >> +	Value type: <none>
>> >> +	Definition: identifies this node as an interrupt controller
>> >> +
>> >> +- #interrupt-cells:
>> >> +	Usage: required
>> >> +	Value type: <u32>
>> >> +	Definition: must be 2. Specifying the pin number and flags, as
>> >defined
>> >> +		    in <dt-bindings/interrupt-controller/irq.h>
>> >> +
>> >> +- gpio-controller:
>> >> +	Usage: required
>> >> +	Value type: <none>
>> >> +	Definition: identifies this node as a gpio controller
>> >> +
>> >> +- #gpio-cells:
>> >> +	Usage: required
>> >> +	Value type: <u32>
>> >> +	Definition: must be 2. Specifying the pin number and flags, as
>> >defined
>> >> +		    in <dt-bindings/gpio/gpio.h>
>> >> +
>> >> +Please refer to ../gpio/gpio.txt and
>> >../interrupt-controller/interrupts.txt for
>> >> +a general description of GPIO and interrupt bindings.
>> >You want to specify gpio-ranges here as well. The property is
>explained
>> >in Section "2.1) gpio- and pin-controller interaction" in
>> >../gpio/gpio.txt
>> >
>> >Without it, the gpio-hogs construct (part of ../gpio/gpio.txt) will
>> >cause
>> >the driver to fail during boot. (try it, ;-) )
>> Would gpio-ranges make sense for this, as the gpio and pinctrl are in
>same block?
>Yes, it's part of the ../gpio/gpio.txt which you link.
>Here's a copy of the relevant section that explains this
>gpio- and pin-controller interaction.
>
>
>|2.1) gpio- and pin-controller interaction
>|-----------------------------------------
>|
>|Some or all of the GPIOs provided by a GPIO controller may be routed
>to pins
>|on the package via a pin controller. This allows muxing those pins
>between
>|GPIO and other functions.
>|It is useful to represent which GPIOs correspond to which pins on
>which pin
>|controllers. The gpio-ranges property described below represents this,
>and
>|contains information structures as follows:
>|
>|       gpio-range-list ::= <single-gpio-range> [gpio-range-list]
>|       single-gpio-range ::= <numeric-gpio-range> | <named-gpio-range>
>|       numeric-gpio-range ::=
>|                       <pinctrl-phandle> <gpio-base> <pinctrl-base>
><count>
>|       named-gpio-range ::= <pinctrl-phandle> <gpio-base> '<0 0>'
>|       pinctrl-phandle : phandle to pin controller node
>|       gpio-base : Base GPIO ID in the GPIO controller
>|       pinctrl-base : Base pinctrl pin ID in the pin controller
>|       count : The number of GPIOs/pins in this range
>|
>|The "pin controller node" mentioned above must conform to the bindings
>|described in ../pinctrl/pinctrl-bindings.txt.
>|...
>
>As for the reason why gpio-ranges is what it is, please look at the ML
>discussion from the "pinctrl: msm: fix gpio-hog related boot issues"
>thread
>on <https://patchwork.kernel.org/patch/10339127/> and the posts by 
>Linus Walleij: <https://patchwork.kernel.org/patch/10339127/#21903101>
>and
>Stephen Boyd: <https://patchwork.kernel.org/patch/10339127/#21867185>.
>(It's quite a bit to take in)
Thanks for the links, makes sense now, I'll add in v2.
>
>> Seems no other qcom pinctrl drivers have it and I'm able to boot
>without it.
>Ok, let's run an experiment. Please remove the gpio-ranges property and
>try
>adding a test gpio-hog to your device's DTS:
>
>something like (I randomly selected GPIO5, but it shouldn't
>matter which gpio you select here. If you know a unused/NC
>pin/gpio, then you can use it instead):
>
>&tlmm {
>	test-hog {
>		gpio-hog;
>		gpios = <5 0>;
>		output-low;
>		line-name = "test hog";
>	};
>};
>
>compile&install it and then watch the kernel on the next boot:
>
>without the gpio-ranges present, it will spew out something along the
>lines of:
>
>| requesting hog GPIO test hog (chip 3000000.pinctrl, offset 5) failed,
>-517
>| gpiochip_add_data: GPIOs 0..114 (3000000.pinctrl) failed to register
>| sdm660-pinctrl 3000000.pinctrl: Failed register gpiochip
>
>The single gpio-hog causes havoc and takes down the sdm660-pinctrl with
>it.
>And every driver that depends on the pinctrl to setup the pin
>muxing/config
>will fail to load as well. (check out /sys/kernel/debug/pinctrl/, it
>will be
>empty.)
Yup
>
>Regards,
>Christian

-- 

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