Re: [PATCH 11/14] arm64: renesas: rzg3s-smarc-som: Invert the logic for SW_SD2_EN macro

[Geert Uytterhoeven]

Hi Claudiu,

On Wed, Dec 6, 2023 at 12:12 PM claudiu beznea <claudiu.beznea@xxxxxxxxx> wrote:
> On 06.12.2023 12:56, Geert Uytterhoeven wrote:
> > On Wed, Dec 6, 2023 at 11:33 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> >> On Mon, Nov 20, 2023 at 8:03 AM Claudiu <claudiu.beznea@xxxxxxxxx> wrote:
> >>> From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> >>>
> >>> The intention of SW_SD2_EN macro was to reflect the state of SW_CONFIG3
> >>> switch available on RZ/G3S Smarc Module. According to documentation SD2
> >>> is enabled when switch is in OFF state. For this, changed the logic of
> >>> marco to map value 0 to switch's OFF state and value 1 to switch's ON
> >>> state. Along with this update the description for each state for better
> >>> understanding.
> >>>
> >>> The value of SW_SD2_EN macro was not changed in file because, according to
> >>> documentation, the default state for this switch is ON.
> >>>
> >>> Fixes: adb4f0c5699c ("arm64: dts: renesas: Add initial support for RZ/G3S SMARC SoM")
> >>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> >>
> >> Thanks for your patch!
> >>
> >>> --- a/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi
> >>> +++ b/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi
> >>> @@ -14,8 +14,8 @@
> >>>   *     0 - SD0 is connected to eMMC
> >>>   *     1 - SD0 is connected to uSD0 card
> >>>   * @SW_SD2_EN:
> >>> - *     0 - SCIF1, SSI0, IRQ0, IRQ1 connected to SoC
> >>> - *     1 - SD2 is connected to SoC
> >>> + *     0 - (switch OFF) SD2 is connected to SoC
> >>> + *     1 - (switch ON)  SCIF1, SSI0, IRQ0, IRQ1 connected to SoC
> >>
> >> I think this is still confusing: SW_SD2_EN refers to an active-low signal
> >> (SW_SD2_EN#) in the schematics.
> >
> > OMG, while the signal is called "SW_SD2_EN#" in the schematics, it is
> > _not_ active-low!
> > SW_D2_EN# drives a STG3692 quad SPDT switch, and SD2 is enabled
> > if SW_D2_EN# is high...
> >
> > The RZ/G3S SMARC Module User Manual says:
> >
> > Signal SW_SD2_EN ON: SD2 is disabled.
> > Signal SW_SD2_EN OFF: SD2 is enabled.
>
> I followed the description in this manual, chapter 2.1.1 SW_CONFIG. The
> idea was that these macros to correspond to individual switches, to match
> that table (describing switches position) with this code as the user in the
> end sets those switches described in table at 2.1.1 w/o necessary going
> deep into schematic (at least in the beginning when trying different
> functionalities).
>
> Do you think it would be better if we will have these macros named
> SWCONFIGX, X in {1, 2, 3, 4, 5, 6} ?

Perhaps. A disadvantage would be that SW_CONFIG%u doesn't
give any indication about its purpose...

> > So whatever we do, something will look odd :-(
> >
> >> Before, SW_SD2_EN used assertion-logic (1 is enabled), and didn't
> >> match the physical signal level.
> >> After your patch, SW_SD2_EN matches the active-low physical level, but
> >> this is not reflected in the name...
> >>
> >>>   */
> >>>  #define SW_SD0_DEV_SEL 1
> >>>  #define SW_SD2_EN      1
> >>> @@ -25,7 +25,7 @@ / {
> >>>
> >>>         aliases {
> >>>                 mmc0 = &sdhi0;
> >>> -#if SW_SD2_EN
> >>> +#if !SW_SD2_EN
> >>
> >> ... so this condition looks really weird.
> >
> > Still, I think the original looks nicer here.
> >
> > So I suggest to keep the original logic, but clarify the position of
> > the switch.
> > Does that make sense?
>
> It will still be odd, AFAICT, as this way as we will map 0 to ON and 1 to
> OFF... A bit counterintuitive.

Most switches on board pull signals LOW when the switch is ON...

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