Re: [PATCH 2/2] gpio: rcar: Add R-Car X5H (R8A78000) support

[Marek Vasut]

On 9/7/26 9:53 AM, Geert Uytterhoeven wrote:

Hello Geert,

> On Sat, 5 Sept 2026 at 23:57, Marek Vasut <marek.vasut@xxxxxxxxxxx> wrote:
> > On 9/4/26 1:15 PM, Geert Uytterhoeven wrote:
> > > > +++ b/drivers/gpio/gpio-rcar.c
> > >
> > > > @@ -65,14 +66,59 @@ struct gpio_rcar_priv {
> > > >
> > > >    #define RCAR_MAX_GPIO_PER_BANK         32
> > > >
> > > > +static inline int gpio_rcar_remap_offset(struct gpio_rcar_priv *p, int *offs)
> > >
> > > IMO passing a pointer to offs complicates the code.  Perhaps pass offs
> > > by value, and return the adjusted offset or a negative error code?
> >
> > I want to avoid that, since if I only return error value, I can then do
> > simple:
> >
> > ret = gpio_rcar_remap_offset(...);
> > if (ret)
> >     return ret;
> >
> > in gpio_rcar_read() and gpio_rcar_write(), which are the only two call
> > sites of this function.
>
> gpio_rcar_read() and gpio_rcar_write() do not return error codes.
> I was thinking of
>
>      offs = gpio_rcar_remap_offset(p, offs);
>      if (offs < 0)
>              return 0;
>
> which is almost the same, but avoids passing offs by address.

Is there any benefit to it, compared to keeping the value and return 
code separate ?

> > > > +{
> > > > +       /* R-Car Gen4 and older do not need any offset remap. */
> > > > +       if (!p->info.has_layout_gen5)
> > > > +               return 0;
> > > > +
> > > > +       /*
> > > > +        * R-Car Gen5 register layout is slightly different and the offsets
> > > > +        * that have to be added to or subtracted from each register offset
> > > > +        * can be divided into five groups, listed below.
> > > > +        */
> > > > +       switch (*offs) {
> > > > +       case IOINTSEL...OUTDT:
> > > > +               return 0;
> > > > +       case INDT:
> > > > +               *offs += 0x10;
> > > > +               return 0;
> > > > +       case INTDT...EDGLEVEL:
> > > > +               fallthrough;
> > > > +       case BOTHEDGE:
> > > > +               *offs += 0x70;
> > > > +               return 0;
> > > > +       case OUTDTSEL:
> > > > +               *offs -= 0x34;
> > > > +               return 0;
> > > > +       case INEN:
> > > > +               *offs -= 0x38;
> > > > +               return 0;
> > > > +       default:
> > > > +               /*
> > > > +                * This here must never be reached, if this is reached, that
> > > > +                * means there is a catastrophic failure in the driver. Skip
> > > > +                * any IO read/write to prevent further damage.
> > > > +                */
> > > > +               WARN_ON(1);
> > >
> > > A build-time failure would be better.  I tried BUILD_BUG() instead,
> > > but unfortunately gcc is not smart enough to notice this case is
> > > never reached.  __always_inline doesn't seem to help either.
> > I had one more idea -- how about we convert the driver to mmio regmap,
> > use opaque register numbers throughout the driver to identify registers
> > to the regmap (maybe not a great idea), and then implement .read/.write
> > callbacks in the regmap_config which instead of doing plain
> > readl()/writel() for register IO would instead do this remapping ?
> > Regmap could validate that the opaque register numbers are only the
> > expected register numbers and reject all the others. Maybe the opaque
> > register numbers could instead of Gen4 register offsets. What do you think ?
>
> That's similar (but more complex?) than the array look-up
> in drivers/tty/serial/sh-sci.c I pointed to before.
> drivers/i2c/busses/i2c-riic.c uses the same method.

Those do not use regmap (drivers/base/regmap/), do they ?

> I.e. just convert the existing register defines into an enum, and use
> that to index a table with the family-specific offsets?
Are we back to the table look up discussion instead of remap function ?