Re: [PATCH 1/3] iio: adc: stm32: fix common clock rate

Jonathan Cameron
2017-07-24T15:04:01Z

On Mon, 24 Jul 2017 09:43:18 +0200
Fabrice Gasnier <fabrice.gasnier@st.com> wrote:

> On 07/23/2017 12:51 PM, Jonathan Cameron wrote:
> > On Tue, 18 Jul 2017 14:35:30 +0200
> > Fabrice Gasnier <fabrice.gasnier@st.com> wrote:
> >
> >> Fixes commit 95e339b6e85d ("iio: adc: stm32: add support for STM32H7")
> >>
> >> Fix common clock rate used then by stm32-adc sub-devices: take common
> >> prescaler into account.
> >> Fix ADC max clock rate on STM32H7 (fADC from datasheet)
> >>
> >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
> > Patch itself is fine, but the description could do with
> > information on what the result of this being wrong is.
>
> Hi Jonathan,
>
> I agree with you and will improve description in v2. I'm thinking of:
>
> Fixes: 95e339b6e85d ("iio: adc: stm32: add support for STM32H7")
>
> ADC clock input is provided to internal prescaler (that decreases its
> frequency). It's then used as reference clock for conversions.
>
> - Fix common clock rate used then by stm32-adc sub-devices. Take common
> prescaler into account. Currently, rate is used to set "boost" mode. It
> may unnecessarily be set. This impacts power consumption.
> - Fix ADC max clock rate on STM32H7 (fADC from datasheet). Currently,
> prescaler may be set too low. This can result in ADC reference clock
> used for conversion to exceed max allowed clock frequency.
>
> >
> > I have no idea if this is a patch I should be sending upstream
> > asap or should hold for the next merge window.
>
> Probably yes... I hope the description is better above? Just to mention
> this impacts stm32h7 adc, device tree node to use it is not yet integrated.

Description is much better thanks. I'll wait for v2 and merge this as a
fix.

Jonathan
>
> Thanks for your review,
> Best Regards,
> Fabrice
> >
> > Thanks,
> >
> > Jonathan
> >> ---
> >> drivers/iio/adc/stm32-adc-core.c | 10 +++++-----
> >> 1 file changed, 5 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c
> >> index e09233b..6096763 100644
> >> --- a/drivers/iio/adc/stm32-adc-core.c
> >> +++ b/drivers/iio/adc/stm32-adc-core.c
> >> @@ -64,7 +64,7 @@
> >> #define STM32H7_CKMODE_MASK GENMASK(17, 16)
> >>
> >> /* STM32 H7 maximum analog clock rate (from datasheet) */
> >> -#define STM32H7_ADC_MAX_CLK_RATE 72000000
> >> +#define STM32H7_ADC_MAX_CLK_RATE 36000000
> >>
> >> /**
> >> * stm32_adc_common_regs - stm32 common registers, compatible dependent data
> >> @@ -148,14 +148,14 @@ static int stm32f4_adc_clk_sel(struct platform_device *pdev,
> >> return -EINVAL;
> >> }
> >>
> >> - priv->common.rate = rate;
> >> + priv->common.rate = rate / stm32f4_pclk_div[i];
> >> val = readl_relaxed(priv->common.base + STM32F4_ADC_CCR);
> >> val &= ~STM32F4_ADC_ADCPRE_MASK;
> >> val |= i << STM32F4_ADC_ADCPRE_SHIFT;
> >> writel_relaxed(val, priv->common.base + STM32F4_ADC_CCR);
> >>
> >> dev_dbg(&pdev->dev, "Using analog clock source at %ld kHz\n",
> >> - rate / (stm32f4_pclk_div[i] * 1000));
> >> + priv->common.rate / 1000);
> >>
> >> return 0;
> >> }
> >> @@ -250,7 +250,7 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
> >>
> >> out:
> >> /* rate used later by each ADC instance to control BOOST mode */
> >> - priv->common.rate = rate;
> >> + priv->common.rate = rate / div;
> >>
> >> /* Set common clock mode and prescaler */
> >> val = readl_relaxed(priv->common.base + STM32H7_ADC_CCR);
> >> @@ -260,7 +260,7 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
> >> writel_relaxed(val, priv->common.base + STM32H7_ADC_CCR);
> >>
> >> dev_dbg(&pdev->dev, "Using %s clock/%d source at %ld kHz\n",
> >> - ckmode ? "bus" : "adc", div, rate / (div * 1000));
> >> + ckmode ? "bus" : "adc", div, priv->common.rate / 1000);
> >>
> >> return 0;
> >> }
> >
>
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