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Fri, 6 Nov 2020 17:57:46 +0100 (CET) Received: from localhost (10.75.127.45) by SFHDAG1NODE3.st.com (10.75.127.3) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 6 Nov 2020 17:57:45 +0100 From: Fabrice Gasnier To: Subject: [PATCH] iio: adc: stm32-adc: adapt clock duty cycle for proper operation Date: Fri, 6 Nov 2020 17:57:26 +0100 Message-ID: <1604681846-31234-1-git-send-email-fabrice.gasnier@st.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 X-Originating-IP: [10.75.127.45] X-ClientProxiedBy: SFHDAG6NODE2.st.com (10.75.127.17) To SFHDAG1NODE3.st.com (10.75.127.3) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312, 18.0.737 definitions=2020-11-06_06:2020-11-05, 2020-11-06 signatures=0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201106_115752_162495_E2B836DB X-CRM114-Status: GOOD ( 20.28 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: olivier.moysan@st.com, alexandre.torgue@st.com, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org For proper operation, STM32 ADC should be used with a clock duty cycle of 50%, in the range of 49% to 51%. Depending on the clock tree, divider can be used in case clock duty cycle is out of this range. In case clk_get_scaled_duty_cycle() returns an error, kindly apply a divider by default (don't make the probe fail). Signed-off-by: Fabrice Gasnier --- drivers/iio/adc/stm32-adc-core.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c index cd870c0..d64a9e8 100644 --- a/drivers/iio/adc/stm32-adc-core.c +++ b/drivers/iio/adc/stm32-adc-core.c @@ -202,7 +202,7 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev, { u32 ckmode, presc, val; unsigned long rate; - int i, div; + int i, div, duty; /* stm32h7 bus clock is common for all ADC instances (mandatory) */ if (!priv->bclk) { @@ -226,6 +226,11 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev, return -EINVAL; } + /* If duty is an error, kindly use at least /2 divider */ + duty = clk_get_scaled_duty_cycle(priv->aclk, 100); + if (duty < 0) + dev_warn(&pdev->dev, "adc clock duty: %d\n", duty); + for (i = 0; i < ARRAY_SIZE(stm32h7_adc_ckmodes_spec); i++) { ckmode = stm32h7_adc_ckmodes_spec[i].ckmode; presc = stm32h7_adc_ckmodes_spec[i].presc; @@ -234,6 +239,13 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev, if (ckmode) continue; + /* + * For proper operation, clock duty cycle range is 49% + * to 51%. Apply at least /2 prescaler otherwise. + */ + if (div == 1 && (duty < 49 || duty > 51)) + continue; + if ((rate / div) <= priv->max_clk_rate) goto out; } @@ -246,6 +258,10 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev, return -EINVAL; } + duty = clk_get_scaled_duty_cycle(priv->bclk, 100); + if (duty < 0) + dev_warn(&pdev->dev, "bus clock duty: %d\n", duty); + for (i = 0; i < ARRAY_SIZE(stm32h7_adc_ckmodes_spec); i++) { ckmode = stm32h7_adc_ckmodes_spec[i].ckmode; presc = stm32h7_adc_ckmodes_spec[i].presc; @@ -254,6 +270,9 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev, if (!ckmode) continue; + if (div == 1 && (duty < 49 || duty > 51)) + continue; + if ((rate / div) <= priv->max_clk_rate) goto out; }