Re: [PATCH v5 5/9] riscv: dts: spacemit: k1: add SD card controller and pinctrl support

["Troy Mitchell" <troy.mitchell@linux.dev>]

On Wed Apr 1, 2026 at 4:53 PM CST, Iker Pedrosa wrote:
> El lun, 30 mar 2026 a las 11:08, Troy Mitchell
> (<troy.mitchell@linux.dev>) escribió:
>>
>> On Mon, Mar 30, 2026 at 16:38:06 CST, Iker Pedrosa wrote:
>> > Add SD card controller infrastructure for SpacemiT K1 SoC with complete
>> > pinctrl support for both standard and UHS modes.
>> >
>> > - Add sdhci0 controller definition with clocks, resets and interrupts
>> > - Add mmc1_cfg pinctrl for 3.3V standard SD operation
>> > - Add mmc1_uhs_cfg pinctrl for 1.8V UHS high-speed operation
>> > - Configure appropriate drive strength and power-source properties
>> >
>> > This provides complete SD card infrastructure that K1-based boards can
>> > enable.
>> >
>> > Tested-by: Anand Moon <linux.amoon@gmail.com>
>> > Tested-by: Trevor Gamblin <tgamblin@baylibre.com>
>> > Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
>> > ---
>> >  arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi | 40 ++++++++++++++++++++++++++++
>> >  arch/riscv/boot/dts/spacemit/k1.dtsi         | 13 +++++++++
>> >  2 files changed, 53 insertions(+)
>> >
>> > diff --git a/arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi b/arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi
>> > index b13dcb10f4d66022d27307de73a6ea3287e97441..8d82011f1af666fb78c282a2abcc0cb88f962053 100644
>> > --- a/arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi
>> > +++ b/arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi
>> > @@ -570,4 +570,44 @@ pwm14-1-pins {
>> >                       drive-strength = <32>;
>> >               };
>> >       };
>> > +
>> > +     mmc1_cfg: mmc1-cfg {
>> > +             mmc1-data-cmd-pins {
>> > +                     pinmux = <K1_PADCONF(104, 0)>,   /* mmc1_d3 */
>> > +                              <K1_PADCONF(105, 0)>,   /* mmc1_d2 */
>> > +                              <K1_PADCONF(106, 0)>,   /* mmc1_d1 */
>> > +                              <K1_PADCONF(107, 0)>,   /* mmc1_d0 */
>> > +                              <K1_PADCONF(108, 0)>;   /* mmc1_cmd */
>> > +                     bias-pull-up = <1>;
>> > +                     drive-strength = <7>;
>> I'm a bit concerned about this value. Looking at the downstream 6.6 code, 3.3V uses DS4,
>> which equals 13mA. Since 7mA maps to DS0, what's the reasoning for using it here?
                ^^^^ wrong current
>> Do we have any documentation or measurement to back this up?
>
> Thank you for catching this! You're absolutely right to question these
> drive strength values.
>
> Looking back at my development process, I remember hitting signal
> integrity issues in the early stages of this driver development. As a
> quick solution, I lowered the drive strength values, which seemed to
> resolve the immediate problems, and I moved on without revisiting the
> electrical characteristics.
>
> After your feedback, I investigated this properly by comparing with
> the vendor kernel. It uses:
> - 3.3V mode: PAD_3V_DS4 (19mA)
> - 1.8V UHS mode: PAD_1V8_DS3 (42mA)
>
> My original values were indeed backwards from both electrical theory
> and proven vendor implementation. Testing with the corrected values
> (19mA/42mA) confirms SD card is working.
>
> I'll send v6 with the corrected drive strength values: drive-strength
> = <19> for 3.3V and drive-strength = <42> for 1.8V UHS modes.
Yes, 19mA for 3.3V and 42mA for 1.8V are correct.
I realized I cited an incorrect value in my previous message (the 13mA).
Please CC me when you send v6.

                                    - Troy