Re: [PATCH v5 5/6] pinctrl: meson: add support of drive-strength-microamp

Hi Guillaume,

On Fri, May 10, 2019 at 10:23 AM Guillaume La Roque
[off-list ref] wrote:

drive-strength-microamp is a new feature needed for G12A SoC.
the default DS setting after boot is usually 500uA and it is not enough for
many functions. We need to be able to set the drive strength to reliably
enable things like MMC, I2C, etc ...

Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>

Reviewed-by: Martin Blumenstingl<martin.blumenstingl@googlemail.com>

the warning messages when printing pinconf-pins (in debugfs) are gone
on my Meson8m2 board so:
Tested-by: Martin Blumenstingl<martin.blumenstingl@googlemail.com>

[...]

+static int meson_pinconf_set_drive_strength(struct meson_pinctrl *pc,
+                                           unsigned int pin,
+                                           u16 drive_strength_ua)
+{
+       struct meson_bank *bank;
+       unsigned int reg, bit, ds_val;
+       int ret;
+
+       if (!pc->reg_ds) {
+               dev_err(pc->dev, "drive-strength not supported\n");
+               return -ENOTSUPP;
+       }
+
+       ret = meson_get_bank(pc, pin, &bank);
+       if (ret)
+               return ret;
+
+       meson_calc_reg_and_bit(bank, pin, REG_DS, &reg, &bit);
+       bit = bit << 1;

I was confused by this shifting (not sure why I haven't noticed this
in earlier revisions). however, it all made sense after I did the
maths for two examples:

BOOT_0 uses drive-strength register 0x0 bits [1:0] so the result
should be "bit = 0"
meson_calc_reg_and_bit returns bit = 0
0 << 1 = 0, so this seems right

BOOT_15 uses drive-strength register 0x0 bits [31:30] so the result
should be "bit = 30"
meson_calc_reg_and_bit returns bit = 15
15 << 1 = 30

so all seems fine, even though it wasn't obvious to me at first sight
that it's all good


Martin