On Thu, 21 Mar 2019 17:47:22 +0100 Fabrice Gasnier <[email protected]> wrote:
> 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]> Applied to the togreg branch of iio.git and pushed out as testing for the autobuilders to play with it. Thanks, Jonathan > --- > 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");
