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

[Geert Uytterhoeven]

Hi Marek,

On Mon, 7 Sept 2026 at 18:37, Marek Vasut <marek.vasut@xxxxxxxxxxx> wrote:
> On 9/7/26 9:53 AM, Geert Uytterhoeven wrote:
> > 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 ?

Naive me (I am not a compiler writer) thinks the compiler may have a
harder time to optimize the code when addresses are involved.

> >>>> +{
> >>>> +       /* 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 ?

No they don't.

> > 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 ?

Yes, I think that's the simplest and best-performing solution: one
extra table look-up (array indexing) in gpio_rcar_{read,write}(),
compared to an extra function call to gpio_rcar_remap_offset().

As a bonus, storing -1 for a non-existing register in the look-up table
would let us get rid of the four existing .has_<reg> booleans, e.g.

   -        if (p->info.has_both_edge_trigger)
   +        if (p->info.regs[BOTHEDGE] >= 0)
                    gpio_rcar_modify_bit(p, BOTHEDGE, hwirq, both);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds