Hi Biju,
On Mon, May 2, 2022 at 8:18 AM Biju Das <biju.das.jz@xxxxxxxxxxxxxx> wrote:
> > Subject: RE: [PATCH] iio: adc: rzg2l_adc: Add support for RZ/G2UL ADC
> > > Subject: [PATCH] iio: adc: rzg2l_adc: Add support for RZ/G2UL ADC
> > >
> > > ADC found on RZ/G2UL SoC is almost identical to RZ/G2L SoC, but
> > > RZ/G2UL has 2 analog input channels compared to 8 channels on RZ/G2L.
> > > Therefore, added a new compatible to handle this difference.
> > >
> > > Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> > > ---
> > > drivers/iio/adc/rzg2l_adc.c | 18 +++++++++++++-----
> > > 1 file changed, 13 insertions(+), 5 deletions(-)
> > >
> > I wonder if this changes is really required. RZ/G2UL can still use the
> > "renesas,rzg2l-adc". As the driver populates the channels depending the
> > number of elements in the array passed in the DTS and not always 8
> > channels. For example on Renesas SMARC EVK only four channels are
> > populated.
>
> For me that restriction is coming from board design, as SoC is capable of handling 8 channels,
> But board design allows only 4.
>
> But on RZ/G2UL SoC, it is capable of handling only 2 channels. Other channels are invalid for RZ/G2UL SoC.
>
> That is the difference.
>
> > With this we don't have to differentiate RZ/G2UL SoC if just add two
> > channel entries in the SoC DTSI and the driver will just create two
> > channels.
>
> > @Geert - your thoughts on this.
It depends on the meaning of the channel subnodes: do they indicate
(a) the number of channels present on the SoC, or (b) the number of
channels used on the board? The DT bindings are not clear about that.
arch/arm64/boot/dts/renesas/r9a07g044.dtsi lists all channels and
doesn't keep any disabled, which suggests (a).
arch/arm64/boot/dts/renesas/rzg2l-smarc-som.dtsi does remove unused
channels, which suggests (b).
Is there any (perhaps performance?) reason we can't just use the number
of channels present in DT? "make dtbs_check" can still validate this
against the SoC-specific compatible value.
Do we need to know at runtime both the number of channels physically
present and the number of channels used? If yes, we either need to
use the SoC-specific compatible value, or add a num-channels property.
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
