| Message ID | 20220221012705.22008-1-billy_tsai@aspeedtech.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] iio: adc: aspeed: Add divider flag to fix incorrect voltage reading. | expand |
On Mon, 21 Feb 2022 at 01:26, Billy Tsai <billy_tsai@aspeedtech.com> wrote: > > The formula for the ADC sampling period in ast2400/ast2500 is: > ADC clock period = PCLK * 2 * (ADC0C[31:17] + 1) * (ADC0C[9:0]) > When ADC0C[9:0] is set to 0 the sampling voltage will be lower than > expected, because the hardware may not have enough time to > charge/discharge to a stable voltage. This patch use the flag > CLK_DIVIDER_ONE_BASED which will use the raw value read from the > register, with the value of zero considered invalid to conform to the > corrected formula. (to answer my own question) ..and this is okay on the 2600, because we do not set need_prescaler = true on that platform. Reviewed-by: Joel Stanley <joel@jms.id.au> > > Fixes: 573803234e72 ("iio: Aspeed ADC") > Reported-by: Konstantin Klubnichkin <kitsok@yandex-team.ru> > Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com> > --- > drivers/iio/adc/aspeed_adc.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c > index a957cad1bfab..ffae64f39221 100644 > --- a/drivers/iio/adc/aspeed_adc.c > +++ b/drivers/iio/adc/aspeed_adc.c > @@ -539,7 +539,9 @@ static int aspeed_adc_probe(struct platform_device *pdev) > data->clk_scaler = devm_clk_hw_register_divider( > &pdev->dev, clk_name, clk_parent_name, scaler_flags, > data->base + ASPEED_REG_CLOCK_CONTROL, 0, > - data->model_data->scaler_bit_width, 0, &data->clk_lock); > + data->model_data->scaler_bit_width, > + data->model_data->need_prescaler ? CLK_DIVIDER_ONE_BASED : 0, > + &data->clk_lock); > if (IS_ERR(data->clk_scaler)) > return PTR_ERR(data->clk_scaler); > > -- > 2.25.1 >
On Mon, 21 Feb 2022 05:45:16 +0000 Joel Stanley <joel@jms.id.au> wrote: > On Mon, 21 Feb 2022 at 01:26, Billy Tsai <billy_tsai@aspeedtech.com> wrote: > > > > The formula for the ADC sampling period in ast2400/ast2500 is: > > ADC clock period = PCLK * 2 * (ADC0C[31:17] + 1) * (ADC0C[9:0]) > > When ADC0C[9:0] is set to 0 the sampling voltage will be lower than > > expected, because the hardware may not have enough time to > > charge/discharge to a stable voltage. This patch use the flag > > CLK_DIVIDER_ONE_BASED which will use the raw value read from the > > register, with the value of zero considered invalid to conform to the > > corrected formula. > > (to answer my own question) > > ..and this is okay on the 2600, because we do not set need_prescaler = > true on that platform. > > Reviewed-by: Joel Stanley <joel@jms.id.au> Applied to the fixes-togreg branch of iio.git. Depending on how timing works out in the coming week I might just pull all the fixes in for the next merge window rather than doing a separate pull request. Thanks, Jonathan > > > > > Fixes: 573803234e72 ("iio: Aspeed ADC") > > Reported-by: Konstantin Klubnichkin <kitsok@yandex-team.ru> > > Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com> > > --- > > drivers/iio/adc/aspeed_adc.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c > > index a957cad1bfab..ffae64f39221 100644 > > --- a/drivers/iio/adc/aspeed_adc.c > > +++ b/drivers/iio/adc/aspeed_adc.c > > @@ -539,7 +539,9 @@ static int aspeed_adc_probe(struct platform_device *pdev) > > data->clk_scaler = devm_clk_hw_register_divider( > > &pdev->dev, clk_name, clk_parent_name, scaler_flags, > > data->base + ASPEED_REG_CLOCK_CONTROL, 0, > > - data->model_data->scaler_bit_width, 0, &data->clk_lock); > > + data->model_data->scaler_bit_width, > > + data->model_data->need_prescaler ? CLK_DIVIDER_ONE_BASED : 0, > > + &data->clk_lock); > > if (IS_ERR(data->clk_scaler)) > > return PTR_ERR(data->clk_scaler); > > > > -- > > 2.25.1 > >
diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c index a957cad1bfab..ffae64f39221 100644 --- a/drivers/iio/adc/aspeed_adc.c +++ b/drivers/iio/adc/aspeed_adc.c @@ -539,7 +539,9 @@ static int aspeed_adc_probe(struct platform_device *pdev) data->clk_scaler = devm_clk_hw_register_divider( &pdev->dev, clk_name, clk_parent_name, scaler_flags, data->base + ASPEED_REG_CLOCK_CONTROL, 0, - data->model_data->scaler_bit_width, 0, &data->clk_lock); + data->model_data->scaler_bit_width, + data->model_data->need_prescaler ? CLK_DIVIDER_ONE_BASED : 0, + &data->clk_lock); if (IS_ERR(data->clk_scaler)) return PTR_ERR(data->clk_scaler);
The formula for the ADC sampling period in ast2400/ast2500 is: ADC clock period = PCLK * 2 * (ADC0C[31:17] + 1) * (ADC0C[9:0]) When ADC0C[9:0] is set to 0 the sampling voltage will be lower than expected, because the hardware may not have enough time to charge/discharge to a stable voltage. This patch use the flag CLK_DIVIDER_ONE_BASED which will use the raw value read from the register, with the value of zero considered invalid to conform to the corrected formula. Fixes: 573803234e72 ("iio: Aspeed ADC") Reported-by: Konstantin Klubnichkin <kitsok@yandex-team.ru> Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com> --- drivers/iio/adc/aspeed_adc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)