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

[Álvaro Fernández Rojas]

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@xxxxxxxxxx> wrote:
> > On Wed, Mar 10, 2021 at 6:09 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> > > On Wed, Mar 10, 2021 at 6:51 PM Rob Herring <robh+dt@xxxxxxxxxx> 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

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.

> We currently have four Broadcom GPIO bindings,
> which are stand alone GPIO blocks and eight Broadcom
> pin controllers that all do GPIO as well.
>
> This family of pin controllers are (as per subject) is
> the bcm63xx series which is a MIPS-based family of SoCs
> found in routers, top bindings in
> Documentation/devicetree/bindings/mips/brcm/soc.txt
> These all have a GPIO block as part of the pin controller
> and the GPIO block is a distinct sub-function of the
> pin controller, and it has up to 32 GPIOs per block,
> hence it has its own subnode inside the pin controller.
>
> This driver follows the pattern of the Ingenic
> pin controller, another MIPS SoC:
> Documentation/devicetree/bindings/pinctrl/ingenic,pinctrl.yaml
>
> Another SoC with several GPIO blocks inside the pin
> controller is SparX5 and that also follows this pattern:
> Documentation/devicetree/bindings/pinctrl/microchip,sparx5-sgpio.yaml
> (This has an example with more than one GPIO block
> inside the pin controller.)
>
> Yours,
> Linus Walleij