linux-kernel - Re: [PATCH v6 03/15] pinctrl: bcm: add bcm63xx base code

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Message-Id: <9022EE3C-47C1-446E-B5D7-EB60934B4E8A@gmail.com>
Date:   Thu, 11 Mar 2021 19:32:37 +0100
From:   Álvaro Fernández Rojas <noltari@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Michael Walle <michael@...le.cc>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Jonas Gorski <jonas.gorski@...il.com>,
        Necip Fazil Yildiran <fazilyildiran@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v6 03/15] pinctrl: bcm: add bcm63xx base code

Hi Rob,

> El 11 mar 2021, a las 19:24, Rob Herring <robh+dt@...nel.org> escribió:
> 
> On Thu, Mar 11, 2021 at 10:00 AM Álvaro Fernández Rojas
> <noltari@...il.com> wrote:
>> 
>> Hi Rob and Linus,
>> 
>> El 11/03/2021 a las 17:13, Linus Walleij escribió:
>>> On Thu, Mar 11, 2021 at 3:58 PM Rob Herring <robh+dt@...nel.org> wrote:
>>>> On Wed, Mar 10, 2021 at 6:09 PM Linus Walleij <linus.walleij@...aro.org> wrote:
>>>>> On Wed, Mar 10, 2021 at 6:51 PM Rob Herring <robh+dt@...nel.org> wrote:
>>>>> 
>>>>>>> +static const struct of_device_id bcm63xx_gpio_of_match[] = {
>>>>>>> +       { .compatible = "brcm,bcm6318-gpio", },
>>>>>>> +       { .compatible = "brcm,bcm6328-gpio", },
>>>>>>> +       { .compatible = "brcm,bcm6358-gpio", },
>>>>>>> +       { .compatible = "brcm,bcm6362-gpio", },
>>>>>>> +       { .compatible = "brcm,bcm6368-gpio", },
>>>>>>> +       { .compatible = "brcm,bcm63268-gpio", },
>>>>>> 
>>>>>> All these would be moved to gpio-mmio.c (or maybe that can have a
>>>>>> fallback compatible?).
>>>>> 
>>>>> This is gpio-regmap.c and it can only be used as a library
>>>>> by a certain driver. gpio-mmio.c can be used stand-alone
>>>>> for certain really simple hardware (though most use that
>>>>> as a library as well).
>>>> 
>>>> I don't really care which one is used, but the problem is that this
>>>> choice is leaking into the binding design.
>>> 
>>> Aha I guess I misunderstood your comment.
>>> 
>>>> The primary problem here is
>>>> once someone uses regmap, then they think they must have a syscon and
>>>> can abandon using 'reg' and normal address properties as Linux happens
>>>> to not use them (currently). I think we really need some better regmap
>>>> vs. mmio handling to eliminate this duplication of foo-mmio and
>>>> foo-regmap drivers and difference in binding design. Not sure exactly
>>>> what that looks like, but basically some sort of 'reg' property to
>>>> regmap creation.
>>> 
>>> I see the problem. Yeah we should try to be more strict around
>>> these things. To me there are syscons and "other regmaps",
>>> where syscon is a real hurdle of registers while "other regmaps"
>>> are just regmaps by convenience.
>>> 
>>> Documentation/devicetree/bindings/mfd/syscon.yaml
>>> describes what a syscon really is so if everyone could
>>> just read the documentation that would be great ...
>>> 
>>>> Given we already have a Broadcom GPIO binding for what looks to be
>>>> similar to this one, I'm left wondering what's the real difference
>>>> here?
>>> 
>>> Which one is similar? I can take a look.
>> 
>> @Linus I think @Rob is referring to brcm,bcm6345-gpio:
>> https://github.com/torvalds/linux/blob/a74e6a014c9d4d4161061f770c9b4f98372ac778/drivers/gpio/gpio-mmio.c#L686
> 
> Well, since it's the bindings we're talking about:
> Documentation/devicetree/bindings/gpio/brcm,bcm6345-gpio.txt
> 
> Which says this:
> "These bindings can be used on any BCM63xx SoC. However, BCM6338 and
> BCM6345 are the only ones which don't need a pinctrl driver."

Yes, I know because I’m the author of that driver…
What I meant at that time is that it could be used temporarily until a proper “full” pinctrl driver was added.

> 
> Not that the 1 in tree user of this is perfect. Seems like it too
> should be a child of a system controller if there's other registers.

There are other registers, but dirout and data registers are contiguous and separate from the others.

> 
>> 
>> However, the real difference between BCM6345 (and BCM6338) is that these
>> SoCs have no pin controller at all, only a GPIO controller:
>> 
>> BCM6345:
>> typedef struct GpioControl {
>>   uint16        unused0;
>>   byte          unused1;
>>   byte          TBusSel;
>>   uint16        unused2;
>>   uint16        GPIODir;
>>   byte          unused3;
>>   byte          Leds;
>>   uint16        GPIOio;
>>   uint32        UartCtl;
>> } GpioControl;
>> 
>> BCM6338:
>> typedef struct GpioControl {
>>   uint32        unused0;
>>   uint32        GPIODir;      /* bits 7:0 */
>>   uint32        unused1;
>>   uint32        GPIOio;       /* bits 7:0 */
>>   uint32        LEDCtrl;
>>   uint32        SpiSlaveCfg;
>>   uint32        vRegConfig;
>> } GpioControl;
>> 
>> BCM6348 and newer also have pinctrl.
>> That's the main difference between that driver @Rob's referring to and
>> the ones in this patch series.

Best regards,
Álvaro.