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

[claudiu beznea]

On 06.12.2023 13:27, Geert Uytterhoeven wrote:
> Hi Claudiu,
> 
> On Wed, Dec 6, 2023 at 12:12 PM claudiu beznea <claudiu.beznea at tuxon.dev> wrote:
>> On 06.12.2023 12:56, Geert Uytterhoeven wrote:
>>> On Wed, Dec 6, 2023 at 11:33 AM Geert Uytterhoeven <geert at linux-m68k.org> wrote:
>>>> On Mon, Nov 20, 2023 at 8:03 AM Claudiu <claudiu.beznea at tuxon.dev> wrote:
>>>>> From: Claudiu Beznea <claudiu.beznea.uj at bp.renesas.com>
>>>>>
>>>>> 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 at bp.renesas.com>
>>>>
>>>> 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...

That's the reason I chose initially to have the signal names instead of
SWCONFIGX.

Now seeing that signal names could be confusing I tend to go with SWCONFIGx
instead.

> 
>>> 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
>