Re: [PATCH] iio: adc: stm32: add oversampling support

From: Jonathan Cameron
Date: Mon Jan 16 2023 - 10:39:05 EST

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In reply to: Olivier Moysan: "[PATCH] iio: adc: stm32: add oversampling support"
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On Mon, 16 Jan 2023 10:03:33 +0100
Olivier Moysan <olivier.moysan@xxxxxxxxxxx> wrote:

> Add oversampling support for STM32H7, STM32MP15 & STM32MP13.
> STM32F4 ADC has no oversampling feature.
>
> The current support of the oversampling feature aims at increasing
> the data SNR, without changing the data resolution.
> As the oversampling by itself increases data resolution,
> a right shift is applied to keep initial resolution.
> Only the oversampling ratio corresponding to a power of two are
> supported here, to get a direct link between right shift and
> oversampling ratio. (2exp(n) ratio <=> n right shift)
>
> The oversampling ratio is shared by all channels, whatever channel type.
> (e.g. single ended or differential).
>
> Oversampling can be configured using IIO ABI:
> - in_voltage_oversampling_ratio_available
> - in_voltage_oversampling_ratio
>
> Signed-off-by: Olivier Moysan <olivier.moysan@xxxxxxxxxxx>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxxxxxxx>

Hi. A few minor suggestions inline.

Also, what is relationship of Fabrice to this patch?
I'd either expect him to have sent it on, or a Co-developed marking
as appropriate.

Thanks,

Jonathan

> ---
> drivers/iio/adc/stm32-adc-core.h | 16 ++++
> drivers/iio/adc/stm32-adc.c | 144 +++++++++++++++++++++++++++++++
> 2 files changed, 160 insertions(+)
>
> diff --git a/drivers/iio/adc/stm32-adc-core.h b/drivers/iio/adc/stm32-adc-core.h
> index 73b2c2e91c08..86a98286eeb3 100644
> --- a/drivers/iio/adc/stm32-adc-core.h
> +++ b/drivers/iio/adc/stm32-adc-core.h
> @@ -91,6 +91,7 @@
> #define STM32H7_ADC_IER 0x04
> #define STM32H7_ADC_CR 0x08
> #define STM32H7_ADC_CFGR 0x0C
> +#define STM32H7_ADC_CFGR2 0x10
> #define STM32H7_ADC_SMPR1 0x14
> #define STM32H7_ADC_SMPR2 0x18
> #define STM32H7_ADC_PCSEL 0x1C
> @@ -160,6 +161,14 @@
> #define STM32H7_DMNGT_SHIFT 0
> #define STM32H7_DMNGT_MASK GENMASK(1, 0)
>
> +/* STM32H7_ADC_CFGR2 bit fields */
> +#define STM32H7_OVSR_SHIFT 16 /* Correspond to OSVR field in datasheet */
> +#define STM32H7_OVSR_MASK GENMASK(25, 16)
> +#define STM32H7_OVSR_BITS 10
> +#define STM32H7_OVSS_SHIFT 5

As below - mostly I'd expect FIELD_PREP / FIELD_GET to be used as they
avoid the need for separate defines for MASK and SHIFT (only MASK ones
are used).

> +#define STM32H7_OVSS_MASK GENMASK(8, 5)
> +#define STM32H7_ROVSE BIT(0)
> +
> enum stm32h7_adc_dmngt {
> STM32H7_DMNGT_DR_ONLY, /* Regular data in DR only */
> STM32H7_DMNGT_DMA_ONESHOT, /* DMA one shot mode */
> @@ -226,6 +235,13 @@ enum stm32h7_adc_dmngt {
> #define STM32MP13_RES_SHIFT 3
> #define STM32MP13_RES_MASK GENMASK(4, 3)
>
> +/* STM32MP13_ADC_CFGR2 bit fields */
> +#define STM32MP13_OVSR_SHIFT 2
> +#define STM32MP13_OVSR_MASK GENMASK(4, 2)
> +#define STM32MP13_OVSR_BITS 3
> +#define STM32MP13_OVSS_SHIFT 5
> +#define STM32MP13_OVSS_MASK GENMASK(8, 5)
> +
> /* STM32MP13_ADC_DIFSEL - bit fields */
> #define STM32MP13_DIFSEL_MASK GENMASK(18, 0)
>
> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> index 45d4e79f8e55..17050875f23d 100644
> --- a/drivers/iio/adc/stm32-adc.c
> +++ b/drivers/iio/adc/stm32-adc.c
> @@ -6,6 +6,7 @@
> * Author: Fabrice Gasnier <fabrice.gasnier@xxxxxx>.
> */
>
> +#include <linux/bitfield.h>
> #include <linux/clk.h>
> #include <linux/debugfs.h>
> #include <linux/delay.h>
> @@ -13,6 +14,7 @@
> #include <linux/dmaengine.h>
> #include <linux/iio/iio.h>
> #include <linux/iio/buffer.h>
> +#include <linux/iio/sysfs.h>

Why? That is only relevant for custom attributes.

> #include <linux/iio/timer/stm32-lptim-trigger.h>
> #include <linux/iio/timer/stm32-timer-trigger.h>
> #include <linux/iio/trigger.h>
> @@ -27,6 +29,7 @@
> #include <linux/platform_device.h>
> #include <linux/pm_runtime.h>
> #include <linux/property.h>
> +#include <linux/util_macros.h>

I'm not immediately seeing anything from here being used.

>
> #include "stm32-adc-core.h"
>
>
...

>
> +static void stm32h7_adc_set_ovs(struct iio_dev *indio_dev, u32 ovs_idx)
> +{
> + struct stm32_adc *adc = iio_priv(indio_dev);
> + u32 ovsr_bits, bits, msk = STM32H7_ROVSE;
> +
> + msk |= STM32H7_OVSR_MASK | STM32H7_OVSS_MASK;

As below.

> + stm32_adc_clr_bits(adc, STM32H7_ADC_CFGR2, msk);
> +
> + if (!ovs_idx)
> + return;
> +
> + bits = STM32H7_ROVSE;
> + ovsr_bits = (1 << ovs_idx) - 1;
> + bits |= ovsr_bits << STM32H7_OVSR_SHIFT;
Good place to FIELD_PREP() and avoid need for SHIFT definitions.

> + bits |= ovs_idx << STM32H7_OVSS_SHIFT;
> +
> + stm32_adc_set_bits(adc, STM32H7_ADC_CFGR2, bits & msk);
> +}
> +
> +static void stm32mp13_adc_set_ovs(struct iio_dev *indio_dev, u32 ovs_idx)
> +{
> + struct stm32_adc *adc = iio_priv(indio_dev);
> + u32 bits, msk = STM32H7_ROVSE;
> +
> + msk |= STM32MP13_OVSR_MASK | STM32MP13_OVSS_MASK;

u32 bits, msk;

msk = STM32H7_ROVSE | STM32MP13_OVSR_MASK | STM32MP13_OVSS_MSK;

is more readable.

> + stm32_adc_clr_bits(adc, STM32H7_ADC_CFGR2, msk);
> +
> + if (!ovs_idx)
> + return;
> +
> + bits = STM32H7_ROVSE;
> + if (ovs_idx - 1)
> + bits |= (ovs_idx - 1) << STM32MP13_OVSR_SHIFT;
> + bits |= ovs_idx << STM32MP13_OVSS_SHIFT;
FIELD_PREP() for all these.

> +
> + stm32_adc_set_bits(adc, STM32H7_ADC_CFGR2, bits & msk);
> +}
> +
> static int stm32h7_adc_exit_pwr_down(struct iio_dev *indio_dev)
> {
> struct stm32_adc *adc = iio_priv(indio_dev);
> @@ -1461,6 +1524,71 @@ static int stm32_adc_single_conv(struct iio_dev *indio_dev,
> return ret;
> }
>
> +static int stm32_adc_write_raw(struct iio_dev *indio_dev, struct iio_chan_spec const *chan,
> + int val, int val2, long mask)
> +{
> + struct stm32_adc *adc = iio_priv(indio_dev);
> + struct device *dev = indio_dev->dev.parent;
> + int nb = adc->cfg->adc_info->num_ovs;
> + u32 idx;
> + int ret;
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> + ret = iio_device_claim_direct_mode(indio_dev);
> + if (ret)
> + return ret;
> +
> + if (val2) {
> + ret = -EINVAL;
> + goto err;
> + }

Do as much as possible outside of the serialization caused
by iio_device_claim_direct_mode.
These sanity checks and indeed the array search can all be done
outside of that and directly return on error.

> +
> + for (idx = 0; idx < nb; idx++)
> + if (adc->cfg->adc_info->oversampling[idx] == val)
> + break;
> +
> + if (idx >= nb) {
> + ret = -EINVAL;
> + goto err;
> + }
> +
> + ret = pm_runtime_resume_and_get(dev);
> + if (ret < 0)
> + goto err;
> +
> + adc->cfg->set_ovs(indio_dev, idx);
> +
> + pm_runtime_mark_last_busy(dev);
> + pm_runtime_put_autosuspend(dev);
> +
> + adc->ovs_idx = idx;
> +
> +err:
> + iio_device_release_direct_mode(indio_dev);
> +
> + return ret;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +static int stm32_adc_read_avail(struct iio_dev *indio_dev, struct iio_chan_spec const *chan,
> + const int **vals, int *type, int *length, long m)

Where it doesn't hurt readability, I'd prefer we keep lines under 80 chars.

> +{
> + struct stm32_adc *adc = iio_priv(indio_dev);
> +
> + switch (m) {
> + case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> + *type = IIO_VAL_INT;
> + *length = adc->cfg->adc_info->num_ovs;
> + *vals = adc->cfg->adc_info->oversampling;
> + return IIO_AVAIL_LIST;
> + default:
> + return -EINVAL;
> + }
> +}
> +

Thanks,

Jonathan

Next message: Maksim Davydov: "[PATCH net 2/2] net/ethernet/chelsio: t4_handle_fw_rpl fix NULL"
Previous message: H. Nikolaus Schaller: "Re: [PATCH] ARM: dts: gta04: fix excess dma channel usage"
In reply to: Olivier Moysan: "[PATCH] iio: adc: stm32: add oversampling support"
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