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

Jonathan Cameron
2017-01-24T18:26:08Z

On 24 January 2017 14:43:56 GMT+00:00, Fabrice Gasnier <fabrice.gasnier@st.com> wrote:
>On 01/22/2017 02:14 PM, Jonathan Cameron wrote:
>> 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?
>
>Hi Jonathan,
>
>Basically no, but there is a limited number of DMA request lines.
>DMA request lines mapping is documented in STM32F4 reference manual
>(DMA1/2 request mapping).
>There may be a situation where user (in dt) assign all DMA channels to
>other IPs. Then only choice would be to fall back using interrupt mode
>for ADC.
>This is why I'd like to keep support for both interrupt and DMA modes.
Ah. Fair enough. Thanks for the explanation. Perhaps a note in the patch description
would give us something to point at in future or even something in the bonding docs?
>
>> 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.
>
>I'll look into it :-)
>
>>
>>> +}
>>> +
>>> +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'.
>
>I'll follow your guidelines and rework this part. I also had some
>doubts
>on this. This is more clear!
>
>Thanks,
>Regards,
>Fabrice
>
>>
>>> +
>>> + 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;
>>>
>>
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