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Commit 2e19ba66 authored by Fabrice Gasnier's avatar Fabrice Gasnier Committed by Jonathan Cameron
Browse files

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: default avatarFabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
parent 57565828

drivers/iio/adc/stm32-dfsdm-core.c

+12 −5
Original line number Diff line number Diff line
@@ -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");