diff options
author | Fabrice Gasnier <fabrice.gasnier@st.com> | 2019-03-21 19:47:22 +0300 |
---|---|---|
committer | Jonathan Cameron <Jonathan.Cameron@huawei.com> | 2019-04-04 22:20:32 +0300 |
commit | 2e19ba661ece580b23115f7eff1e5fad25317172 (patch) | |
tree | 69286b366246f5ff954eabc6f47eea1b9c2bf389 | |
parent | 57565828adf56e1a3200dd488ad86c84673a361e (diff) | |
download | linux-2e19ba661ece580b23115f7eff1e5fad25317172.tar.xz |
iio: adc: stm32-dfsdm: make spi_master_freq more accurate
Current ckout divider may be set to a value that makes ckout to exceed
spi-max-frequency. Rather use lower value (e.g. round up divider when
ckout isn't accurate).
Also when the SPI clock isn't accurate, 'spi_master_freq' is filled in
with expected frequency. Use computed value instead to be more accurate:
- e.g. source clock / (CKOUTDIV + 1)
Enforce checks on the divider: ckoutdiv range can be from 1-255 to provide
divider of 2-256.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
-rw-r--r-- | drivers/iio/adc/stm32-dfsdm-core.c | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/drivers/iio/adc/stm32-dfsdm-core.c b/drivers/iio/adc/stm32-dfsdm-core.c index bf089f5d6225..472b809ebf94 100644 --- a/drivers/iio/adc/stm32-dfsdm-core.c +++ b/drivers/iio/adc/stm32-dfsdm-core.c @@ -199,7 +199,7 @@ static int stm32_dfsdm_parse_of(struct platform_device *pdev, { struct device_node *node = pdev->dev.of_node; struct resource *res; - unsigned long clk_freq; + unsigned long clk_freq, divider; unsigned int spi_freq, rem; int ret; @@ -243,13 +243,20 @@ static int stm32_dfsdm_parse_of(struct platform_device *pdev, return 0; } - priv->spi_clk_out_div = div_u64_rem(clk_freq, spi_freq, &rem) - 1; - if (!priv->spi_clk_out_div) { - /* spi_clk_out_div == 0 means ckout is OFF */ + divider = div_u64_rem(clk_freq, spi_freq, &rem); + /* Round up divider when ckout isn't precise, not to exceed spi_freq */ + if (rem) + divider++; + + /* programmable divider is in range of [2:256] */ + if (divider < 2 || divider > 256) { dev_err(&pdev->dev, "spi-max-frequency not achievable\n"); return -EINVAL; } - priv->dfsdm.spi_master_freq = spi_freq; + + /* SPI clock output divider is: divider = CKOUTDIV + 1 */ + priv->spi_clk_out_div = divider - 1; + priv->dfsdm.spi_master_freq = clk_freq / (priv->spi_clk_out_div + 1); if (rem) { dev_warn(&pdev->dev, "SPI clock not accurate\n"); |