iio: adc: meson: add support for the GXLX SoC

The SARADC IP on the GXLX SoC itself is identical to the one found on
GXL SoCs. However, GXLX SoCs require poking the first three bits in the
MESON_SAR_ADC_REG12 register to get the three MPLL clocks (used as clock
generators for the audio frequencies) to work.

The reason why there are MPLL clock bits in the ADC register space is
entirely unknown and it seems that nobody is able to comment on this.
So clearly mark this as a workaround and add a warning so users are
notified that this workaround can change (once we know what these bits
actually do).

Tested-by: Christian Hewitt <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
Signed-off-by: Martin Blumenstingl <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/meson_saradc.c

···
 	#define MESON_SAR_ADC_REG11_EOC				BIT(1)
 	#define MESON_SAR_ADC_REG11_VREF_SEL			BIT(0)
 
+#define MESON_SAR_ADC_REG12					0x30
+	#define MESON_SAR_ADC_REG12_MPLL0_UNKNOWN		BIT(0)
+	#define MESON_SAR_ADC_REG12_MPLL1_UNKNOWN		BIT(1)
+	#define MESON_SAR_ADC_REG12_MPLL2_UNKNOWN		BIT(2)
+
 #define MESON_SAR_ADC_REG13					0x34
 	#define MESON_SAR_ADC_REG13_12BIT_CALIBRATION_MASK	GENMASK(13, 8)
 
···
 	u8					cmv_select;
 	u8					adc_eoc;
 	enum meson_sar_adc_vref_sel		vref_voltage;
+	bool					enable_mpll_clock_workaround;
 };
 
 struct meson_sar_adc_data {
···
 				    priv->param->cmv_select);
 		regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG11,
 				   MESON_SAR_ADC_REG11_CMV_SEL, regval);
+
+		if (priv->param->enable_mpll_clock_workaround) {
+			dev_warn(dev,
+				 "Enabling unknown bits to make the MPLL clocks work. This may change so always update dtbs and kernel together\n");
+			regmap_write(priv->regmap, MESON_SAR_ADC_REG12,
+				     MESON_SAR_ADC_REG12_MPLL0_UNKNOWN |
+				     MESON_SAR_ADC_REG12_MPLL1_UNKNOWN |
+				     MESON_SAR_ADC_REG12_MPLL2_UNKNOWN);
+		}
 	}
 
 	ret = clk_set_parent(priv->adc_sel_clk, priv->clkin);
···
 	.cmv_select = 1,
 };
 
+static const struct meson_sar_adc_param meson_sar_adc_gxlx_param = {
+	.has_bl30_integration = true,
+	.clock_rate = 1200000,
+	.regmap_config = &meson_sar_adc_regmap_config_gxbb,
+	.resolution = 12,
+	.disable_ring_counter = 1,
+	.vref_voltage = 1,
+	.cmv_select = true,
+	.enable_mpll_clock_workaround = true,
+};
+
 static const struct meson_sar_adc_param meson_sar_adc_axg_param = {
 	.has_bl30_integration = true,
 	.clock_rate = 1200000,
···
 	.name = "meson-gxl-saradc",
 };
 
+static const struct meson_sar_adc_data meson_sar_adc_gxlx_data = {
+	.param = &meson_sar_adc_gxlx_param,
+	.name = "meson-gxlx-saradc",
+};
+
 static const struct meson_sar_adc_data meson_sar_adc_gxm_data = {
 	.param = &meson_sar_adc_gxl_param,
 	.name = "meson-gxm-saradc",
···
 	}, {
 		.compatible = "amlogic,meson-gxl-saradc",
 		.data = &meson_sar_adc_gxl_data,
+	}, {
+		.compatible = "amlogic,meson-gxlx-saradc",
+		.data = &meson_sar_adc_gxlx_data,
 	}, {
 		.compatible = "amlogic,meson-gxm-saradc",
 		.data = &meson_sar_adc_gxm_data,