Re: [PATCH 5/7] iio: adc: stm32: add optional dma support

Jonathan Cameron
2017-01-22T13:15:04Z

On 19/01/17 13:34, Fabrice Gasnier wrote:
> Add optional DMA support to STM32 ADC.
> Use dma cyclic mode with at least two periods.
>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
What is the point going forward in supporting non dma buffered reads at all?
Is there hardware that doesn't have DMA support?
Just strikes me that the driver would be slight simpler if we dropped that
support.

Various comments inline. Mostly around crossing the boundary to fetch
from the IIO specific buffer (indio_dev->buffer). That should never be
used directly as we can have multiple consumers of the datastream so
the numbers you get from that may represent only part of what is going on.

> ---
> drivers/iio/adc/Kconfig | 2 +
> drivers/iio/adc/stm32-adc-core.c | 1 +
> drivers/iio/adc/stm32-adc-core.h | 2 +
> drivers/iio/adc/stm32-adc.c | 209 ++++++++++++++++++++++++++++++++++++---
> 4 files changed, 202 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 9a7b090..2a2ef78 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -444,12 +444,14 @@ config ROCKCHIP_SARADC
> config STM32_ADC_CORE
> tristate "STMicroelectronics STM32 adc core"
> depends on ARCH_STM32 || COMPILE_TEST
> + depends on HAS_DMA
> depends on OF
> depends on REGULATOR
> select IIO_BUFFER
> select MFD_STM32_TIMERS
> select IIO_STM32_TIMER_TRIGGER
> select IIO_TRIGGERED_BUFFER
> + select IRQ_WORK
> help
> Select this option to enable the core driver for STMicroelectronics
> STM32 analog-to-digital converter (ADC).
> diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c
> index 4214b0c..22b7c93 100644
> --- a/drivers/iio/adc/stm32-adc-core.c
> +++ b/drivers/iio/adc/stm32-adc-core.c
> @@ -201,6 +201,7 @@ static int stm32_adc_probe(struct platform_device *pdev)
> priv->common.base = devm_ioremap_resource(&pdev->dev, res);
> if (IS_ERR(priv->common.base))
> return PTR_ERR(priv->common.base);
> + priv->common.phys_base = res->start;
>
> priv->vref = devm_regulator_get(&pdev->dev, "vref");
> if (IS_ERR(priv->vref)) {
> diff --git a/drivers/iio/adc/stm32-adc-core.h b/drivers/iio/adc/stm32-adc-core.h
> index 081fa5f..2ec7abb 100644
> --- a/drivers/iio/adc/stm32-adc-core.h
> +++ b/drivers/iio/adc/stm32-adc-core.h
> @@ -42,10 +42,12 @@
> /**
> * struct stm32_adc_common - stm32 ADC driver common data (for all instances)
> * @base: control registers base cpu addr
> + * @phys_base: control registers base physical addr
> * @vref_mv: vref voltage (mv)
> */
> struct stm32_adc_common {
> void __iomem *base;
> + phys_addr_t phys_base;
> int vref_mv;
> };
>
> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> index 9753c39..3439f4c 100644
> --- a/drivers/iio/adc/stm32-adc.c
> +++ b/drivers/iio/adc/stm32-adc.c
> @@ -21,6 +21,8 @@
>
> #include <linux/clk.h>
> #include <linux/delay.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/dmaengine.h>
> #include <linux/iio/iio.h>
> #include <linux/iio/buffer.h>
> #include <linux/iio/timer/stm32-timer-trigger.h>
> @@ -29,6 +31,7 @@
> #include <linux/iio/triggered_buffer.h>
> #include <linux/interrupt.h>
> #include <linux/io.h>
> +#include <linux/irq_work.h>
> #include <linux/module.h>
> #include <linux/platform_device.h>
> #include <linux/of.h>
> @@ -69,6 +72,8 @@
> #define STM32F4_EXTSEL_SHIFT 24
> #define STM32F4_EXTSEL_MASK GENMASK(27, 24)
> #define STM32F4_EOCS BIT(10)
> +#define STM32F4_DDS BIT(9)
> +#define STM32F4_DMA BIT(8)
> #define STM32F4_ADON BIT(0)
>
> /* STM32F4_ADC_SQR1 - bit fields */
> @@ -165,6 +170,11 @@ struct stm32_adc_trig_info {
> * @bufi: data buffer index
> * @num_conv: expected number of scan conversions
> * @exten: external trigger config (enable/polarity)
> + * @work: irq work used to call trigger poll routine
> + * @dma_chan: dma channel
> + * @rx_buf: dma rx buffer cpu address
> + * @rx_dma_buf: dma rx buffer bus address
> + * @rx_buf_sz: dma rx buffer size
> */
> struct stm32_adc {
> struct stm32_adc_common *common;
> @@ -177,6 +187,11 @@ struct stm32_adc {
> int bufi;
> int num_conv;
> enum stm32_adc_exten exten;
> + struct irq_work work;
> + struct dma_chan *dma_chan;
> + u8 *rx_buf;
> + dma_addr_t rx_dma_buf;
> + int rx_buf_sz;
> };
>
> /**
> @@ -332,10 +347,20 @@ static void stm32_adc_conv_irq_disable(struct stm32_adc *adc)
> /**
> * stm32_adc_start_conv() - Start conversions for regular channels.
> * @adc: stm32 adc instance
> + *
> + * Start conversions for regular channels.
> + * Also take care of normal or DMA mode. DMA is used in circular mode for
> + * regular conversions, in IIO buffer modes. Rely on rx_buf as raw
> + * read doesn't use dma, but direct DR read.
> */
> static void stm32_adc_start_conv(struct stm32_adc *adc)
> {
> stm32_adc_set_bits(adc, STM32F4_ADC_CR1, STM32F4_SCAN);
> +
> + if (adc->rx_buf)
> + stm32_adc_set_bits(adc, STM32F4_ADC_CR2,
> + STM32F4_DMA | STM32F4_DDS);
> +
> stm32_adc_set_bits(adc, STM32F4_ADC_CR2, STM32F4_EOCS | STM32F4_ADON);
>
> /* Wait for Power-up time (tSTAB from datasheet) */
> @@ -353,6 +378,10 @@ static void stm32_adc_stop_conv(struct stm32_adc *adc)
>
> stm32_adc_clr_bits(adc, STM32F4_ADC_CR1, STM32F4_SCAN);
> stm32_adc_clr_bits(adc, STM32F4_ADC_CR2, STM32F4_ADON);
> +
> + if (adc->rx_buf)
> + stm32_adc_clr_bits(adc, STM32F4_ADC_CR2,
> + STM32F4_DMA | STM32F4_DDS);
> }
>
> /**
> @@ -689,19 +718,138 @@ static int stm32_adc_debugfs_reg_access(struct iio_dev *indio_dev,
> .driver_module = THIS_MODULE,
> };
>
> +static int stm32_adc_dma_residue(struct stm32_adc *adc)
> +{
> + struct dma_tx_state state;
> + enum dma_status status;
> +
> + if (!adc->rx_buf)
> + return 0;
> +
> + status = dmaengine_tx_status(adc->dma_chan,
> + adc->dma_chan->cookie,
> + &state);
> + if (status == DMA_IN_PROGRESS) {
> + /* Residue is size in bytes from end of buffer */
> + int i = adc->rx_buf_sz - state.residue;
> + int size;
> +
> + /* Return available bytes */
> + if (i >= adc->bufi)
> + size = i - adc->bufi;
> + else
> + size = adc->rx_buf_sz - adc->bufi + i;
> +
> + return size;
> + }
> +
> + return 0;
> +}
> +
> +static void stm32_adc_dma_irq_work(struct irq_work *work)
> +{
> + struct stm32_adc *adc = container_of(work, struct stm32_adc, work);
> + struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +
> + /**
> + * iio_trigger_poll calls generic_handle_irq(). So, it requires hard
> + * irq context, and cannot be called directly from dma callback,
> + * dma cb has to schedule this work instead.
> + */
> + iio_trigger_poll(indio_dev->trig);
This is nasty ;) iio_trigger_poll_chained is your friend. It is missnamed.
If you only need to call the threaded part of the pollfunc (and I think you
can construct it so you do) then it will call it without needing to bounce
back into interrupt context.

> +}
> +
> +static void stm32_adc_dma_buffer_done(void *data)
> +{
> + struct stm32_adc *adc = data;
> +
> + /* invoques iio_trigger_poll() from hard irq context */
> + irq_work_queue(&adc->work);
> +}
> +
> static int stm32_adc_buffer_preenable(struct iio_dev *indio_dev)
> {
> struct stm32_adc *adc = iio_priv(indio_dev);
> + struct dma_async_tx_descriptor *desc;
> + struct dma_slave_config config;
> + dma_cookie_t cookie;
> + int ret, size, watermark;
>
> /* Reset adc buffer index */
> adc->bufi = 0;
>
> - /* Allocate adc buffer */
> - adc->buffer = kzalloc(indio_dev->scan_bytes, GFP_KERNEL);
> - if (!adc->buffer)
> + if (!adc->dma_chan) {
> + /* Allocate adc buffer */
> + adc->buffer = kzalloc(indio_dev->scan_bytes, GFP_KERNEL);
> + if (!adc->buffer)
> + return -ENOMEM;
> +
> + return 0;
> + }
> +
> + /*
> + * Allocate at least twice the buffer size for dma cyclic transfers, so
> + * we can work with at least two dma periods. There should be :
> + * - always one buffer (period) dma is working on
> + * - one buffer (period) driver can push with iio_trigger_poll().
> + */
> + size = indio_dev->buffer->bytes_per_datum * indio_dev->buffer->length;
> + size = max(indio_dev->scan_bytes * 2, size);
Hmm. There is a bit of a weird mix going on here. Firstly, you may have more
than one consumer buffer, the one you are checking is only the one directly
associated with the IIO userspace interface.

So scan_bytes is the right value to use for both of these statements.
The buffer length is typically not knowable either or relevant here.
If you are ultimately going to deal with watermarks there is an interface
to guide read sizes based on that but this isn't it.

So basically device should never know anything at all about the software
buffer. All info should pass through the core which knows about all the
consumers hanging off this interface (and the demux that is going on to
feed them all).

Some drivers provide additional info to allow the modifying of the
precise hardware watermark being used. That's an acceptable form of
'tweak'.

> +
> + adc->rx_buf = dma_alloc_coherent(adc->dma_chan->device->dev,
> + PAGE_ALIGN(size), &adc->rx_dma_buf,
> + GFP_KERNEL);
> + if (!adc->rx_buf)
> return -ENOMEM;
> + adc->rx_buf_sz = size;
> + watermark = indio_dev->buffer->bytes_per_datum
> + * indio_dev->buffer->watermark;
> + watermark = max(indio_dev->scan_bytes, watermark);
> + watermark = rounddown(watermark, indio_dev->scan_bytes);
> +
> + dev_dbg(&indio_dev->dev, "%s size=%d watermark=%d\n", __func__, size,
> + watermark);
> +
> + /* Configure DMA channel to read data register */
> + memset(&config, 0, sizeof(config));
> + config.src_addr = (dma_addr_t)adc->common->phys_base;
> + config.src_addr += adc->offset + STM32F4_ADC_DR;
> + config.src_addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;
> +
> + ret = dmaengine_slave_config(adc->dma_chan, &config);
> + if (ret)
> + goto config_err;
> +
> + /* Prepare a DMA cyclic transaction */
> + desc = dmaengine_prep_dma_cyclic(adc->dma_chan,
> + adc->rx_dma_buf,
> + size, watermark,
> + DMA_DEV_TO_MEM,
> + DMA_PREP_INTERRUPT);
> + if (!desc) {
> + ret = -ENODEV;
> + goto config_err;
> + }
> +
> + desc->callback = stm32_adc_dma_buffer_done;
> + desc->callback_param = adc;
> +
> + cookie = dmaengine_submit(desc);
> + if (dma_submit_error(cookie)) {
> + ret = dma_submit_error(cookie);
> + goto config_err;
> + }
> +
> + /* Issue pending DMA requests */
> + dma_async_issue_pending(adc->dma_chan);
>
> return 0;
> +
> +config_err:
> + dma_free_coherent(adc->dma_chan->device->dev, PAGE_ALIGN(size),
> + adc->rx_buf, adc->rx_dma_buf);
> +
> + return ret;
> }
>
> static int stm32_adc_buffer_postenable(struct iio_dev *indio_dev)
> @@ -719,7 +867,8 @@ static int stm32_adc_buffer_postenable(struct iio_dev *indio_dev)
> if (ret < 0)
> return ret;
>
> - stm32_adc_conv_irq_enable(adc);
> + if (!adc->dma_chan)
> + stm32_adc_conv_irq_enable(adc);
> stm32_adc_start_conv(adc);
>
> return 0;
> @@ -731,7 +880,8 @@ static int stm32_adc_buffer_predisable(struct iio_dev *indio_dev)
> int ret;
>
> stm32_adc_stop_conv(adc);
> - stm32_adc_conv_irq_disable(adc);
> + if (!adc->dma_chan)
> + stm32_adc_conv_irq_disable(adc);
>
> ret = iio_triggered_buffer_predisable(indio_dev);
> if (ret < 0)
> @@ -748,7 +898,16 @@ static int stm32_adc_buffer_postdisable(struct iio_dev *indio_dev)
> {
> struct stm32_adc *adc = iio_priv(indio_dev);
>
> - kfree(adc->buffer);
> + if (!adc->dma_chan) {
> + kfree(adc->buffer);
> + } else {
> + dmaengine_terminate_all(adc->dma_chan);
> + irq_work_sync(&adc->work);
> + dma_free_coherent(adc->dma_chan->device->dev,
> + PAGE_ALIGN(adc->rx_buf_sz),
> + adc->rx_buf, adc->rx_dma_buf);
> + adc->rx_buf = NULL;
> + }
> adc->buffer = NULL;
>
> return 0;
> @@ -769,15 +928,31 @@ static irqreturn_t stm32_adc_trigger_handler(int irq, void *p)
>
> dev_dbg(&indio_dev->dev, "%s bufi=%d\n", __func__, adc->bufi);
>
> - /* reset buffer index */
> - adc->bufi = 0;
> - iio_push_to_buffers_with_timestamp(indio_dev, adc->buffer,
> - pf->timestamp);
> + if (!adc->dma_chan) {
> + /* reset buffer index */
> + adc->bufi = 0;
> + iio_push_to_buffers_with_timestamp(indio_dev, adc->buffer,
> + pf->timestamp);
> + } else {
> + int residue = stm32_adc_dma_residue(adc);
> +
> + while (residue >= indio_dev->scan_bytes) {
> + adc->buffer = (u16 *)&adc->rx_buf[adc->bufi];
> + iio_push_to_buffers_with_timestamp(indio_dev,
> + adc->buffer,
> + pf->timestamp);
> + residue -= indio_dev->scan_bytes;
> + adc->bufi += indio_dev->scan_bytes;
> + if (adc->bufi >= adc->rx_buf_sz)
> + adc->bufi = 0;
> + }
> + }
>
> iio_trigger_notify_done(indio_dev->trig);
>
> /* re-enable eoc irq */
> - stm32_adc_conv_irq_enable(adc);
> + if (!adc->dma_chan)
> + stm32_adc_conv_irq_enable(adc);
>
> return IRQ_HANDLED;
> }
> @@ -910,13 +1085,17 @@ static int stm32_adc_probe(struct platform_device *pdev)
> if (ret < 0)
> goto err_clk_disable;
>
> + adc->dma_chan = dma_request_slave_channel(&indio_dev->dev, "rx");
> + if (adc->dma_chan)
> + init_irq_work(&adc->work, stm32_adc_dma_irq_work);
> +
> ret = iio_triggered_buffer_setup(indio_dev,
> &iio_pollfunc_store_time,
> &stm32_adc_trigger_handler,
> &stm32_adc_buffer_setup_ops);
> if (ret) {
> dev_err(&pdev->dev, "buffer setup failed\n");
> - goto err_clk_disable;
> + goto err_dma_disable;
> }
>
> ret = iio_device_register(indio_dev);
> @@ -930,6 +1109,10 @@ static int stm32_adc_probe(struct platform_device *pdev)
> err_buffer_cleanup:
> iio_triggered_buffer_cleanup(indio_dev);
>
> +err_dma_disable:
> + if (adc->dma_chan)
> + dma_release_channel(adc->dma_chan);
> +
> err_clk_disable:
> clk_disable_unprepare(adc->clk);
>
> @@ -943,6 +1126,8 @@ static int stm32_adc_remove(struct platform_device *pdev)
>
> iio_device_unregister(indio_dev);
> iio_triggered_buffer_cleanup(indio_dev);
> + if (adc->dma_chan)
> + dma_release_channel(adc->dma_chan);
> clk_disable_unprepare(adc->clk);
>
> return 0;
>