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Date:   Sun, 14 May 2017 16:12:49 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Eugen Hristev <eugen.hristev@...rochip.com>,
        nicolas.ferre@...rochip.com, alexandre.belloni@...e-electrons.com,
        linux-iio@...r.kernel.org, lars@...afoo.de,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] iio: adc: at91-sama5d2_adc: add hw trigger and
 buffer support

On 11/05/17 07:09, Ludovic Desroches wrote:
> On Wed, May 10, 2017 at 11:49:07AM +0300, Eugen Hristev wrote:
>> Hello,
>>
>> Thanks for the suggestions and reply.
>>
>> Please see my answers inline
>>
>> Eugen
>>
>> On 07.05.2017 18:01, Jonathan Cameron wrote:
>>> On 04/05/17 13:13, Eugen Hristev wrote:
>>>> Added support for the external hardware trigger on pin ADTRG,
>>>> integrated the three possible edge triggers into the subsystem
>>>> and created buffer management for data retrieval
>>>>
>>>> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
>>>> ---
>>>>    Changes in v2:
>>>>   - Moved buffer allocation and freeing into the preenable and postdisable
>>>>     callbacks.
>>>>     We have a total of scan bytes that can vary a lot depending on each channel
>>>>     enabled at a certain point.
>>> How much?  Having dynamic allocations are likely to prove just as costly as you'll
>>> almost always end up allocating a lot more than you ask for.
>>>
>>> I'm counting worst case of 18x 2byte channels + timestamp = 48 bytes.
>>> A quick google suggests you'll always allocate 32 bytes whatever with slab
>>> (lower for slob). So not a huge saving...
>>>
>>> Worth the hassle?
>>
>>
>> I will modify the allocation of scan_bytes to make it static.
>>
>>>
>>>>   - made the at91 trigger list part of state structure
>>>>   - made the iio trigger list preallocated in state structure
>>>>   - moved irq enabling/disabling into the try_reenable callback
>>> I'd have liked a little explanation on why we need to explicitly disable
>>> the irq.  It will have little effect it if triggers too often as the
>>> trigger consumers are all oneshot anyway.
>>
>> Regarding the irq, the discussion is a bit longer.
>>
>> As it is now, the interrupt is not a oneshot threaded one, because only
>> the top half handler is installed, and the threaded one is NULL.
>> Calling trigger_poll without disabling the interrupt will make the
>> handler loop, so that is the reason for disabling and reenabling
>> the interrupt.
>>
>> One solution is to change it to oneshot threaded interrupt and call
>> trigger_poll_chained to make it a nested handling. This will make a
>> longer response time for conversions though.
>>
>> One other option is to do irq_save and irq_restore before issuing the
>> trigger poll, but that limits the usability of the trigger by any
>> other device I guess.
>>
>> I did the behavior with disabling and enabling the interrupt considering
>> the old at91 driver and the stm32-adc driver which looks to be fairly
>> similar with this implementation.
>>
>> Can you please advise on which approach you think it's best for this
>> driver ?
>> So I can try that, and resend the patch.
Leave it as is.  Thanks for the explanation.
>>
>>>>   - on trigger disable must write disable registries as well
>>> Basically looks good. A few questions inline.
>>>
>>> Jonathan
>>>>
>>>>   drivers/iio/adc/at91-sama5d2_adc.c | 231 ++++++++++++++++++++++++++++++++++++-
>>>>   1 file changed, 228 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
>>>> index e10dca3..11f5570 100644
>>>> --- a/drivers/iio/adc/at91-sama5d2_adc.c
>>>> +++ b/drivers/iio/adc/at91-sama5d2_adc.c
>>>> @@ -23,8 +23,15 @@
>>>>   #include <linux/platform_device.h>
>>>>   #include <linux/sched.h>
>>>>   #include <linux/wait.h>
>>>> +#include <linux/slab.h>
>>>> +
>>>>   #include <linux/iio/iio.h>
>>>>   #include <linux/iio/sysfs.h>
>>>> +#include <linux/iio/buffer.h>
>>>> +#include <linux/iio/trigger.h>
>>>> +#include <linux/iio/trigger_consumer.h>
>>>> +#include <linux/iio/triggered_buffer.h>
>>>> +
>>>>   #include <linux/regulator/consumer.h>
>>>>
>>>>   /* Control Register */
>>>> @@ -132,6 +139,17 @@
>>>>   #define AT91_SAMA5D2_PRESSR	0xbc
>>>>   /* Trigger Register */
>>>>   #define AT91_SAMA5D2_TRGR	0xc0
>>>> +/* Mask for TRGMOD field of TRGR register */
>>>> +#define AT91_SAMA5D2_TRGR_TRGMOD_MASK GENMASK(2, 0)
>>>> +/* No trigger, only software trigger can start conversions */
>>>> +#define AT91_SAMA5D2_TRGR_TRGMOD_NO_TRIGGER 0
>>>> +/* Trigger Mode external trigger rising edge */
>>>> +#define AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_RISE 1
>>>> +/* Trigger Mode external trigger falling edge */
>>>> +#define AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_FALL 2
>>>> +/* Trigger Mode external trigger any edge */
>>>> +#define AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_ANY 3
>>>> +
>>>>   /* Correction Select Register */
>>>>   #define AT91_SAMA5D2_COSR	0xd0
>>>>   /* Correction Value Register */
>>>> @@ -145,14 +163,20 @@
>>>>   /* Version Register */
>>>>   #define AT91_SAMA5D2_VERSION	0xfc
>>>>
>>>> +#define AT91_SAMA5D2_HW_TRIG_CNT 3
>>>> +#define AT91_SAMA5D2_SINGLE_CHAN_CNT 12
>>>> +#define AT91_SAMA5D2_DIFF_CHAN_CNT 6
>>>> +
>>>>   #define AT91_SAMA5D2_CHAN_SINGLE(num, addr)				\
>>>>   	{								\
>>>>   		.type = IIO_VOLTAGE,					\
>>>>   		.channel = num,						\
>>>>   		.address = addr,					\
>>>> +		.scan_index = num,					\
>>>>   		.scan_type = {						\
>>>>   			.sign = 'u',					\
>>>>   			.realbits = 12,					\
>>>> +			.storagebits = 16,				\
>>>>   		},							\
>>>>   		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
>>>>   		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
>>>> @@ -168,9 +192,11 @@
>>>>   		.channel = num,						\
>>>>   		.channel2 = num2,					\
>>>>   		.address = addr,					\
>>>> +		.scan_index = num + AT91_SAMA5D2_SINGLE_CHAN_CNT,	\
>>>>   		.scan_type = {						\
>>>>   			.sign = 's',					\
>>>>   			.realbits = 12,					\
>>>> +			.storagebits = 16,				\
>>>>   		},							\
>>>>   		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
>>>>   		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
>>>> @@ -188,18 +214,25 @@ struct at91_adc_soc_info {
>>>>   	unsigned			max_sample_rate;
>>>>   };
>>>>
>>>> +struct at91_adc_trigger {
>>>> +	char				*name;
>>>> +	unsigned int			trgmod_value;
>>>> +};
>>>> +
>>>>   struct at91_adc_state {
>>>>   	void __iomem			*base;
>>>>   	int				irq;
>>>>   	struct clk			*per_clk;
>>>>   	struct regulator		*reg;
>>>>   	struct regulator		*vref;
>>>> +	u16				*buffer;
>>>>   	int				vref_uv;
>>>>   	const struct iio_chan_spec	*chan;
>>>>   	bool				conversion_done;
>>>>   	u32				conversion_value;
>>>>   	struct at91_adc_soc_info	soc_info;
>>>>   	wait_queue_head_t		wq_data_available;
>>>> +	struct iio_trigger		*trig[AT91_SAMA5D2_HW_TRIG_CNT];
>>>>   	/*
>>>>   	 * lock to prevent concurrent 'single conversion' requests through
>>>>   	 * sysfs.
>>>> @@ -207,6 +240,21 @@ struct at91_adc_state {
>>>>   	struct mutex			lock;
>>>>   };
>>>>
>>>> +static const struct at91_adc_trigger at91_adc_trigger_list[] = {
>>>> +	{
>>>> +		.name = "external-rising",
>>>> +		.trgmod_value = AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_RISE,
>>>> +	},
>>>> +	{
>>>> +		.name = "external-falling",
>>>> +		.trgmod_value = AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_FALL,
>>>> +	},
>>>> +	{
>>>> +		.name = "external-any",
>>>> +		.trgmod_value = AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_ANY,
>>>> +	},
>>> Hmm. Should this be a userspace configurable option?  Feels rather like
>>> it is an element of the hardware - reflecting the characteristics of some
>>> hardware device sat on the pin.
>> The user can choose from sysfs which trigger
>> is best suited for the use case, since all
>> three triggers are provided and can be connected to the buffer.
>> It reflects more the triggering capability of the ADC rather than
>> any different hardware device sitting on the pin
> 
> I am also in favour of a userspace configurable option. For sure it's
> hardware related but on our board we only provide a trigger pin, we
> don't know which hardware the customer will put on this pin.
hmm. OK I'm persuaded I think.

Could do this with devicetree overlays or similar.

So follow up question is whether this is the right interface.
Can all 3 run at once sensibly?  If not are we not looking at a control
parameter for a single trigger?
> 
> Regards
> 
> Ludovic
> 
>>
>>>> +};
>>>> +
>>>>   static const struct iio_chan_spec at91_adc_channels[] = {
>>>>   	AT91_SAMA5D2_CHAN_SINGLE(0, 0x50),
>>>>   	AT91_SAMA5D2_CHAN_SINGLE(1, 0x54),
>>>> @@ -226,8 +274,168 @@ static const struct iio_chan_spec at91_adc_channels[] = {
>>>>   	AT91_SAMA5D2_CHAN_DIFF(6, 7, 0x68),
>>>>   	AT91_SAMA5D2_CHAN_DIFF(8, 9, 0x70),
>>>>   	AT91_SAMA5D2_CHAN_DIFF(10, 11, 0x78),
>>>> +	IIO_CHAN_SOFT_TIMESTAMP(AT91_SAMA5D2_SINGLE_CHAN_CNT
>>>> +				+ AT91_SAMA5D2_DIFF_CHAN_CNT + 1),
>>>>   };
>>>>
>>>> +static int at91_adc_configure_trigger(struct iio_trigger *trig, bool state)
>>>> +{
>>>> +	struct iio_dev *indio = iio_trigger_get_drvdata(trig);
>>>> +	struct at91_adc_state *st = iio_priv(indio);
>>>> +	u32 status = at91_adc_readl(st, AT91_SAMA5D2_TRGR);
>>>> +	u8 bit;
>>>> +	int i;
>>>> +
>>>> +	/* clear TRGMOD */
>>>> +	status &= ~AT91_SAMA5D2_TRGR_TRGMOD_MASK;
>>>> +
>>>> +	if (state)
>>>> +		for (i = 0; i < AT91_SAMA5D2_HW_TRIG_CNT; i++) {
>>>> +			if (!strstr(trig->name,
>>>> +				    at91_adc_trigger_list[i].name)) {
>>>> +				status |= at91_adc_trigger_list[i].trgmod_value;
>>>> +				break;
>>>> +			}
>>>> +		}
>>>> +
>>>> +	/* set/unset hw trigger */
>>>> +	at91_adc_writel(st, AT91_SAMA5D2_TRGR, status);
>>>> +
>>>> +	for_each_set_bit(bit, indio->active_scan_mask, indio->num_channels) {
>>>> +		struct iio_chan_spec const *chan = indio->channels + bit;
>>>> +
>>>> +		if (state) {
>>>> +			at91_adc_writel(st, AT91_SAMA5D2_CHER,
>>>> +					BIT(chan->channel));
>>>> +			at91_adc_writel(st, AT91_SAMA5D2_IER,
>>>> +					BIT(chan->channel));
>>>> +		} else {
>>>> +			at91_adc_writel(st, AT91_SAMA5D2_IDR,
>>>> +					BIT(chan->channel));
>>>> +			at91_adc_writel(st, AT91_SAMA5D2_CHDR,
>>>> +					BIT(chan->channel));
>>>> +		}
>>>> +	}
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static int at91_adc_reenable_trigger(struct iio_trigger *trig)
>>>> +{
>>>> +	struct iio_dev *indio = iio_trigger_get_drvdata(trig);
>>>> +	struct at91_adc_state *st = iio_priv(indio);
>>>> +
>>>> +	enable_irq(st->irq);
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static const struct iio_trigger_ops at91_adc_trigger_ops = {
>>>> +	.owner = THIS_MODULE,
>>>> +	.set_trigger_state = &at91_adc_configure_trigger,
>>>> +	.try_reenable = &at91_adc_reenable_trigger,
>>>> +};
>>>> +
>>>> +static int at91_adc_buffer_preenable(struct iio_dev *indio_dev)
>>>> +{
>>>> +	struct at91_adc_state *st = iio_priv(indio_dev);
>>>> +
>>>> +	st->buffer = kmalloc(indio_dev->scan_bytes, GFP_KERNEL);Why allocate it here?  Presumably the biggest it can get is fairly
>>> small?  Unless very large, just make sure you allocate enough
>>> directly in st in the first place.
>>
>> Yes , as discussed above will change to static allocation.
>>
>>>
>>>> +
>>>> +	if (!st->buffer)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static int at91_adc_buffer_postdisable(struct iio_dev *indio_dev)
>>>> +{
>>>> +	struct at91_adc_state *st = iio_priv(indio_dev);
>>>> +
>>>> +	kfree(st->buffer);
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static const struct iio_buffer_setup_ops at91_buffer_setup_ops = {
>>>> +	.preenable = &at91_adc_buffer_preenable,
>>>> +	.postenable = &iio_triggered_buffer_postenable,
>>>> +	.predisable = &iio_triggered_buffer_predisable,
>>>> +	.postdisable = &at91_adc_buffer_postdisable,
>>>> +};
>>>> +
>>>> +static struct iio_trigger *at91_adc_allocate_trigger(struct iio_dev *indio,
>>>> +						     char *trigger_name)
>>>> +{
>>>> +	struct iio_trigger *trig;
>>>> +	int ret;
>>>> +
>>>> +	trig = devm_iio_trigger_alloc(&indio->dev, "%s-dev%d-%s", indio->name,
>>>> +				      indio->id, trigger_name);
>>>> +	if (!trig)
>>>> +		return NULL;
>>>> +
>>>> +	trig->dev.parent = indio->dev.parent;
>>>> +	iio_trigger_set_drvdata(trig, indio);
>>>> +	trig->ops = &at91_adc_trigger_ops;
>>>> +
>>>> +	ret = devm_iio_trigger_register(&indio->dev, trig);
>>>> +
>>>> +	if (ret)
>>>> +		return NULL;
>>>> +
>>>> +	return trig;
>>>> +}
>>>> +
>>>> +static int at91_adc_trigger_init(struct iio_dev *indio)
>>>> +{
>>>> +	struct at91_adc_state *st = iio_priv(indio);
>>>> +	int i;
>>>> +
>>>> +	for (i = 0; i < AT91_SAMA5D2_HW_TRIG_CNT; i++) {
>>>> +		st->trig[i] = at91_adc_allocate_trigger(indio,
>>>> +						at91_adc_trigger_list[i].name);
>>>> +		if (!st->trig[i]) {
>>>> +			dev_err(&indio->dev,
>>>> +				"could not allocate trigger %d\n", i);
>>>> +			return -ENOMEM;
>>>> +		}
>>>> +	}
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static irqreturn_t at91_adc_trigger_handler(int irq, void *p)
>>>> +{
>>>> +	struct iio_poll_func *pf = p;
>>>> +	struct iio_dev *indio = pf->indio_dev;
>>>> +	struct at91_adc_state *st = iio_priv(indio);
>>>> +	int i = 0;
>>>> +	u8 bit;
>>>> +
>>>> +	for_each_set_bit(bit, indio->active_scan_mask, indio->num_channels) {
>>>> +		struct iio_chan_spec const *chan = indio->channels + bit;
>>>> +
>>>> +		st->buffer[i] = at91_adc_readl(st, chan->address);
>>>> +		i++;
>>>> +	}
>>>> +
>>>> +	iio_push_to_buffers_with_timestamp(indio, st->buffer, pf->timestamp);
>>>> +
>>>> +	iio_trigger_notify_done(indio->trig);
>>>> +
>>>> +	/* Needed to ACK the DRDY interruption */
>>>> +	at91_adc_readl(st, AT91_SAMA5D2_LCDR);
>>>> +
>>>> +	return IRQ_HANDLED;
>>>> +}
>>>> +
>>>> +static int at91_adc_buffer_init(struct iio_dev *indio)
>>>> +{
>>>> +	return devm_iio_triggered_buffer_setup(&indio->dev, indio,
>>>> +			&iio_pollfunc_store_time,
>>>> +			&at91_adc_trigger_handler, &at91_buffer_setup_ops);
>>>> +}
>>>> +
>>>>   static unsigned at91_adc_startup_time(unsigned startup_time_min,
>>>>   				      unsigned adc_clk_khz)
>>>>   {
>>>> @@ -293,14 +501,19 @@ static irqreturn_t at91_adc_interrupt(int irq, void *private)
>>>>   	u32 status = at91_adc_readl(st, AT91_SAMA5D2_ISR);
>>>>   	u32 imr = at91_adc_readl(st, AT91_SAMA5D2_IMR);
>>>>
>>>> -	if (status & imr) {
>>>> +	if (!(status & imr))
>>>> +		return IRQ_NONE;
>>>> +
>>>> +	if (iio_buffer_enabled(indio)) {
>>>> +		disable_irq_nosync(irq);
>>>> +		iio_trigger_poll(indio->trig);
>>>> +	} else {
>>>>   		st->conversion_value = at91_adc_readl(st, st->chan->address);
>>>>   		st->conversion_done = true;
>>>>   		wake_up_interruptible(&st->wq_data_available);
>>>> -		return IRQ_HANDLED;
>>>>   	}
>>>>
>>>> -	return IRQ_NONE;
>>>> +	return IRQ_HANDLED;
>>>>   }
>>>>
>>>>   static int at91_adc_read_raw(struct iio_dev *indio_dev,
>>>> @@ -499,6 +712,18 @@ static int at91_adc_probe(struct platform_device *pdev)
>>>>
>>>>   	platform_set_drvdata(pdev, indio_dev);
>>>>
>>>> +	ret = at91_adc_buffer_init(indio_dev);
>>>> +	if (ret < 0) {
>>>> +		dev_err(&pdev->dev, "couldn't initialize the buffer.\n");
>>>> +		goto per_clk_disable_unprepare;
>>>> +	}
>>>> +
>>>> +	ret = at91_adc_trigger_init(indio_dev);
>>>> +	if (ret < 0) {
>>>> +		dev_err(&pdev->dev, "couldn't setup the triggers.\n");
>>>> +		goto per_clk_disable_unprepare;
>>>> +	}
>>>> +
>>>>   	ret = iio_device_register(indio_dev);
>>>>   	if (ret < 0)
>>>>   		goto per_clk_disable_unprepare;
>>>>
>>>
>> --
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