On Fri, Jun 04, 2021 at 11:31:07AM +0200, Linus Walleij wrote:
> Hi Jonathan!
>
> thanks for your patch!
>
> On Wed, Jun 2, 2021 at 2:04 PM Jonathan Neuschäfer
> <j.neuschaefer@xxxxxxx> wrote:
> >
> > This driver is heavily based on the one for NPCM7xx, because the WPCM450
> > is a predecessor of those SoCs.
> >
> > The biggest difference is in how the GPIO controller works. In the
> > WPCM450, the GPIO registers are not organized in multiple banks, but
> > rather placed continually into the same register block, and the driver
> > reflects this.
>
> This is unfortunate because now you can't use GPIO_GENERIC anymore.
>
> > Some functionality implemented in the hardware was (for now) left unused
> > in the driver, specifically blinking and pull-up/down.
> >
> > Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@xxxxxxx>
>
> (...)
>
> > +config PINCTRL_WPCM450
> > + bool "Pinctrl and GPIO driver for Nuvoton WPCM450"
> > + depends on (ARCH_WPCM450 || COMPILE_TEST) && OF
> > + select PINMUX
> > + select PINCONF
> > + select GENERIC_PINCONF
> > + select GPIOLIB
> > + select GPIO_GENERIC
>
> You are not using GPIO_GENERIC
I'll remove the this line (depending on the outcome of the rest of the
discussion).
>
> > +struct wpcm450_port {
> > + /* Range of GPIOs in this port */
> > + u8 base;
> > + u8 length;
> > +
> > + /* Register offsets (0 = register doesn't exist in this port) */
> > + u8 cfg0, cfg1, cfg2;
> > + u8 blink;
> > + u8 dataout, datain;
> > +};
>
> If you used to have "GPIO banks" and you now have
> "GPIO ports" what is the difference? Why can't these ports
> just be individula gpio_chip:s with their own device tree
> nodes inside the pin controller node?
The naming difference is a fairly arbitrary choice by me.
The real difference is in how the GPIO registers are laid out.
On NPCM7xx, there are blocks of registers at +0, +0x1000, +0x2000,
etc., and within a block, the registers have the same offsets.
On WPCM450, the registers are all mushed together as tightly as
possible[1], so that (a) the ports/banks don't start at nice addresses,
and (b) the register layout can't be predicted from the offset of the
first register in a port (because not all ports have all registers).
> If you split it up then you can go back to using
> GPIO_GENERIC with bgpio_init() again which is a
> big win.
>
> All you seem to be doing is setting consecutive
> bits in a register by offset, which is what GPIO_GENERIC
> is for, just that it assumes offset is always from zero.
> If you split it into individual gpio_chips per register
> then you get this nice separation and code reuse.
Indeed, if I keep the wpcm450_ports table but use it to call bgpio_init()
with the right register addresses, I think bgpio_init() can work.
Thanks,
Jonathan Neuschäfer
[1]: https://github.com/neuschaefer/wpcm450/wiki/GPIOs-and-pinmux#gpio
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