linux-kernel - Re: [PATCH 1/8] counter/ti-eqep: implement over/underflow events

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Date:   Wed, 27 Oct 2021 10:23:13 -0500
From:   David Lechner <david@...hnology.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     linux-iio@...r.kernel.org, Robert Nelson <robertcnelson@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] counter/ti-eqep: implement over/underflow events

On 10/25/21 2:13 AM, William Breathitt Gray wrote:
> On Sat, Oct 16, 2021 at 08:33:36PM -0500, David Lechner wrote:
>> This adds support to the TI eQEP counter driver for subscribing to
>> overflow and underflow events using the counter chrdev interface.
>>
>> Since this is the first event added, this involved adding an irq
>> handler. Also, additional range checks had to be added to the ceiling
>> attribute to avoid infinite interrupts.
>>
>> Signed-off-by: David Lechner <david@...hnology.com>
> 
> Hi David,
> 
> This looks functionally okay, but I have a couple minor comments inline.
> 
>> ---
>>   drivers/counter/ti-eqep.c | 119 +++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 117 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/counter/ti-eqep.c b/drivers/counter/ti-eqep.c
>> index 09817c953f9a..b7c79435e127 100644
>> --- a/drivers/counter/ti-eqep.c
>> +++ b/drivers/counter/ti-eqep.c
>> @@ -7,6 +7,7 @@
>>   
>>   #include <linux/bitops.h>
>>   #include <linux/counter.h>
>> +#include <linux/interrupt.h>
>>   #include <linux/kernel.h>
>>   #include <linux/mod_devicetable.h>
>>   #include <linux/module.h>
>> @@ -67,6 +68,44 @@
>>   #define QEPCTL_UTE		BIT(1)
>>   #define QEPCTL_WDE		BIT(0)
>>   
>> +#define QEINT_UTO		BIT(11)
>> +#define QEINT_IEL		BIT(10)
>> +#define QEINT_SEL		BIT(9)
>> +#define QEINT_PCM		BIT(8)
>> +#define QEINT_PCR		BIT(7)
>> +#define QEINT_PCO		BIT(6)
>> +#define QEINT_PCU		BIT(5)
>> +#define QEINT_WTO		BIT(4)
>> +#define QEINT_QDC		BIT(3)
>> +#define QEINT_PHE		BIT(2)
>> +#define QEINT_PCE		BIT(1)
>> +
>> +#define QFLG_UTO		BIT(11)
>> +#define QFLG_IEL		BIT(10)
>> +#define QFLG_SEL		BIT(9)
>> +#define QFLG_PCM		BIT(8)
>> +#define QFLG_PCR		BIT(7)
>> +#define QFLG_PCO		BIT(6)
>> +#define QFLG_PCU		BIT(5)
>> +#define QFLG_WTO		BIT(4)
>> +#define QFLG_QDC		BIT(3)
>> +#define QFLG_PHE		BIT(2)
>> +#define QFLG_PCE		BIT(1)
>> +#define QFLG_INT		BIT(0)
>> +
>> +#define QCLR_UTO		BIT(11)
>> +#define QCLR_IEL		BIT(10)
>> +#define QCLR_SEL		BIT(9)
>> +#define QCLR_PCM		BIT(8)
>> +#define QCLR_PCR		BIT(7)
>> +#define QCLR_PCO		BIT(6)
>> +#define QCLR_PCU		BIT(5)
>> +#define QCLR_WTO		BIT(4)
>> +#define QCLR_QDC		BIT(3)
>> +#define QCLR_PHE		BIT(2)
>> +#define QCLR_PCE		BIT(1)
>> +#define QCLR_INT		BIT(0)
>> +
>>   /* EQEP Inputs */
>>   enum {
>>   	TI_EQEP_SIGNAL_QEPA,	/* QEPA/XCLK */
>> @@ -233,12 +272,46 @@ static int ti_eqep_action_read(struct counter_device *counter,
>>   	}
>>   }
>>   
>> +static int ti_eqep_events_configure(struct counter_device *counter)
>> +{
>> +	struct ti_eqep_cnt *priv = counter->priv;
>> +	struct counter_event_node *event_node;
>> +	u32 qeint = 0;
>> +
>> +	list_for_each_entry(event_node, &counter->events_list, l) {
>> +		switch (event_node->event) {
>> +		case COUNTER_EVENT_OVERFLOW:
>> +			qeint |= QEINT_PCO;
>> +			break;
>> +		case COUNTER_EVENT_UNDERFLOW:
>> +			qeint |= QEINT_PCU;
>> +			break;
>> +		}
>> +	}
>> +
>> +	return regmap_write_bits(priv->regmap16, QEINT, ~0, qeint);
>> +}
>> +
>> +static int ti_eqep_watch_validate(struct counter_device *counter,
>> +				  const struct counter_watch *watch)
>> +{
>> +	switch (watch->event) {
>> +	case COUNTER_EVENT_OVERFLOW:
>> +	case COUNTER_EVENT_UNDERFLOW:
>> +		return 0;
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +}
>> +
>>   static const struct counter_ops ti_eqep_counter_ops = {
>>   	.count_read	= ti_eqep_count_read,
>>   	.count_write	= ti_eqep_count_write,
>>   	.function_read	= ti_eqep_function_read,
>>   	.function_write	= ti_eqep_function_write,
>>   	.action_read	= ti_eqep_action_read,
>> +	.events_configure = ti_eqep_events_configure,
>> +	.watch_validate	= ti_eqep_watch_validate,
>>   };
>>   
>>   static int ti_eqep_position_ceiling_read(struct counter_device *counter,
>> @@ -260,11 +333,17 @@ static int ti_eqep_position_ceiling_write(struct counter_device *counter,
>>   					  u64 ceiling)
>>   {
>>   	struct ti_eqep_cnt *priv = counter->priv;
>> +	u32 qposmax = ceiling;
>>   
>> -	if (ceiling != (u32)ceiling)
>> +	/* ensure that value fits in 32-bit register */
>> +	if (qposmax != ceiling)
>>   		return -ERANGE;
>>   
>> -	regmap_write(priv->regmap32, QPOSMAX, ceiling);
>> +	/* protect against infinite overflow interrupts */
>> +	if (qposmax == 0)
>> +		return -EINVAL;
> 
> Would you be able to explain this scenario a bit further? My expectation
> would be that an overflow event would only occur if the position
> increased past the ceiling (i.e. increased to greater than 0). Of
> course, running the device with a ceiling of 0 effectively guarantees
> overflow eventss with every movement, but I would expect a stationary
> device to sit with a position of 0 and thus no overflow events.
> 

This is just the way the hardware works. I discovered this the first
time I enabled interrupts. Even if you clear the interrupt, it is
triggered again immediately when QPOSMAX == 0.