Re: [RFC PATCH 1/2] dt-bindings: i2c: renesas,rcar-i2c: document SMBusAlert usage

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Wolfram,

On Sat, Aug 31, 2024 at 5:31 PM Wolfram Sang
<wsa+renesas@sang-engineering.com> wrote:
> > IIUIC, this is not a property of the hardware, but a side-channel
> > independent from the actual I2C controller hardware? Then a generic
> > "smbus-alert-gpios" property sounds more appropriate to me.
>
> It is not generic. While it is true that most I2C controllers do need
> GPIOs as a side channel, there are controllers having...
>
> > BTW, are you aware of any I2C controller having a dedicated input pin
> > for this?
>
> ... this. Check 'i2c-stm32f7.c' or 'i2c-xlp9xx.c'.

OK...

Still, this interrupt is not a property of the R-Car i2C hardware block,
so it should not be modelled as such.

To me, this looks similar to hardware flow control on serial ports:
some ports support this in hardware, other ports need to use GPIOs,
or board designers may still decide to use a GPIO anyway.

See Documentation/devicetree/bindings/serial/serial.yaml and
drivers/tty/serial/serial_mctrl_gpio.c, which uses GPIO interrupts.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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