GX SoCs use a 1.2 MHz ADC clock, while the older SoCs use a 1.14 MHz
clock.
A comment in the driver from Amlogic's GPL kernel says that it's
running at 1.28 MHz. However, it's actually programming a divider of
20 + 1. With a XTAL clock of 24 MHz this results in a frequency of
1.14 MHz. (their calculation might be based on a 27 MHz XTAL clock,
but this is not what we have on the Meson8 and Meson8b SoCs).
The ADC was still working with the 1.2MHz clock. In my own tests I did
not see a difference between 1.2 and 1.14 MHz (regardless of the clock
frequency used, the ADC results were identical).
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
---
drivers/iio/adc/meson_saradc.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
index 7dc7d297a0fc..fa3c1378c2c9 100644
--- a/drivers/iio/adc/meson_saradc.c
+++ b/drivers/iio/adc/meson_saradc.c
@@ -221,6 +221,7 @@ enum meson_sar_adc_chan7_mux_sel {
struct meson_sar_adc_data {
bool has_bl30_integration;
+ unsigned long clock_rate;
u32 bandgap_reg;
unsigned int resolution;
const char *name;
@@ -684,7 +685,7 @@ static int meson_sar_adc_init(struct iio_dev *indio_dev)
return ret;
}
- ret = clk_set_rate(priv->adc_clk, 1200000);
+ ret = clk_set_rate(priv->adc_clk, priv->data->clock_rate);
if (ret) {
dev_err(indio_dev->dev.parent,
"failed to set adc clock rate\n");
@@ -867,6 +868,7 @@ static const struct iio_info meson_sar_adc_iio_info = {
static const struct meson_sar_adc_data meson_sar_adc_meson8_data = {
.has_bl30_integration = false,
+ .clock_rate = 1150000,
.bandgap_reg = MESON_SAR_ADC_DELTA_10,
.regmap_config = &meson_sar_adc_regmap_config_meson8,
.resolution = 10,
@@ -875,6 +877,7 @@ static const struct meson_sar_adc_data meson_sar_adc_meson8_data = {
static const struct meson_sar_adc_data meson_sar_adc_meson8b_data = {
.has_bl30_integration = false,
+ .clock_rate = 1150000,
.bandgap_reg = MESON_SAR_ADC_DELTA_10,
.regmap_config = &meson_sar_adc_regmap_config_meson8,
.resolution = 10,
@@ -883,6 +886,7 @@ static const struct meson_sar_adc_data meson_sar_adc_meson8b_data = {
static const struct meson_sar_adc_data meson_sar_adc_gxbb_data = {
.has_bl30_integration = true,
+ .clock_rate = 1200000,
.bandgap_reg = MESON_SAR_ADC_REG11,
.regmap_config = &meson_sar_adc_regmap_config_gxbb,
.resolution = 10,
@@ -891,6 +895,7 @@ static const struct meson_sar_adc_data meson_sar_adc_gxbb_data = {
static const struct meson_sar_adc_data meson_sar_adc_gxl_data = {
.has_bl30_integration = true,
+ .clock_rate = 1200000,
.bandgap_reg = MESON_SAR_ADC_REG11,
.regmap_config = &meson_sar_adc_regmap_config_gxbb,
.resolution = 12,
@@ -899,6 +904,7 @@ static const struct meson_sar_adc_data meson_sar_adc_gxl_data = {
static const struct meson_sar_adc_data meson_sar_adc_gxm_data = {
.has_bl30_integration = true,
+ .clock_rate = 1200000,
.bandgap_reg = MESON_SAR_ADC_REG11,
.regmap_config = &meson_sar_adc_regmap_config_gxbb,
.resolution = 12,
--
2.15.0
--
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