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 <[email protected]> --- Changes in v2: - rework the way to determine ckoutdiv bitfield: deal with divider directly to explicitly handle the rounding, the range constraints of 2-256 and the divider = ckoutdiv + 1. --- drivers/iio/adc/stm32-dfsdm-core.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/drivers/iio/adc/stm32-dfsdm-core.c b/drivers/iio/adc/stm32-dfsdm-core.c index bf089f5..472b809 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"); -- 2.7.4
