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Date: Mon, 25 Oct 2021 16:13:14 +0900
From: William Breathitt Gray <vilhelm.gray@...il.com>
To: David Lechner <david@...hnology.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 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.
> +
> + regmap_write(priv->regmap32, QPOSMAX, qposmax);
>
> return 0;
> }
> @@ -349,6 +428,25 @@ static struct counter_count ti_eqep_counts[] = {
> },
> };
>
> +static irqreturn_t ti_eqep_irq_handler(int irq, void *dev_id)
> +{
> + struct ti_eqep_cnt *priv = dev_id;
> + struct counter_device *counter = &priv->counter;
> + u32 qflg;
> +
> + regmap_read(priv->regmap16, QFLG, &qflg);
> +
> + if (qflg & QFLG_PCO)
> + counter_push_event(counter, COUNTER_EVENT_OVERFLOW, 0);
> +
> + if (qflg & QFLG_PCU)
> + counter_push_event(counter, COUNTER_EVENT_UNDERFLOW, 0);
> +
> + regmap_set_bits(priv->regmap16, QCLR, ~0);
I agree with Jonathan here, it looks like this is unconditionally
clearing all interrupt flags but it's possible new ones could have
appear between the time after you read QFLG to here. Is it possible to
clear just the interrupt flags you've handled here instead of all?
William Breathitt Gray
> +
> + return IRQ_HANDLED;
> +}
> +
> static const struct regmap_config ti_eqep_regmap32_config = {
> .name = "32-bit",
> .reg_bits = 32,
> @@ -371,6 +469,7 @@ static int ti_eqep_probe(struct platform_device *pdev)
> struct ti_eqep_cnt *priv;
> void __iomem *base;
> int err;
> + int irq;
>
> priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> if (!priv)
> @@ -390,6 +489,15 @@ static int ti_eqep_probe(struct platform_device *pdev)
> if (IS_ERR(priv->regmap16))
> return PTR_ERR(priv->regmap16);
>
> + irq = platform_get_irq(pdev, 0);
> + if (irq < 0)
> + return irq;
> +
> + err = devm_request_threaded_irq(dev, irq, NULL, ti_eqep_irq_handler,
> + IRQF_ONESHOT, dev_name(dev), priv);
> + if (err < 0)
> + return err;
> +
> priv->counter.name = dev_name(dev);
> priv->counter.parent = dev;
> priv->counter.ops = &ti_eqep_counter_ops;
> @@ -409,6 +517,13 @@ static int ti_eqep_probe(struct platform_device *pdev)
> pm_runtime_enable(dev);
> pm_runtime_get_sync(dev);
>
> + /*
> + * We can end up with an interupt infinite loop (interrupts triggered
> + * as soon as they are cleared) if we leave this at the default value
> + * of 0 and events are enabled.
> + */
> + regmap_write(priv->regmap32, QPOSMAX, UINT_MAX);
> +
> err = counter_register(&priv->counter);
> if (err < 0) {
> pm_runtime_put_sync(dev);
> --
> 2.25.1
>
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