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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>
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@ -199,7 +199,7 @@ static int stm32_dfsdm_parse_of(struct platform_device *pdev,
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{
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struct device_node *node = pdev->dev.of_node;
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struct resource *res;
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unsigned long clk_freq;
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unsigned long clk_freq, divider;
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unsigned int spi_freq, rem;
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int ret;
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@ -243,13 +243,20 @@ static int stm32_dfsdm_parse_of(struct platform_device *pdev,
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return 0;
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}
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priv->spi_clk_out_div = div_u64_rem(clk_freq, spi_freq, &rem) - 1;
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if (!priv->spi_clk_out_div) {
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/* spi_clk_out_div == 0 means ckout is OFF */
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divider = div_u64_rem(clk_freq, spi_freq, &rem);
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/* Round up divider when ckout isn't precise, not to exceed spi_freq */
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if (rem)
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divider++;
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/* programmable divider is in range of [2:256] */
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if (divider < 2 || divider > 256) {
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dev_err(&pdev->dev, "spi-max-frequency not achievable\n");
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return -EINVAL;
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}
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priv->dfsdm.spi_master_freq = spi_freq;
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/* SPI clock output divider is: divider = CKOUTDIV + 1 */
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priv->spi_clk_out_div = divider - 1;
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priv->dfsdm.spi_master_freq = clk_freq / (priv->spi_clk_out_div + 1);
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if (rem) {
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dev_warn(&pdev->dev, "SPI clock not accurate\n");
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