Input: pm8941-pwrkey - add software key press debouncing support

On certain PMICs, an unexpected assertion of KPDPWR_DEB (the
positive logic hardware debounced power key signal) may be seen
during the falling edge of KPDPWR_N (i.e. a power key press) when
it occurs close to the rising edge of SLEEP_CLK. This then
triggers a spurious KPDPWR interrupt.

Handle this issue by adding software debouncing support to ignore
key events that occur within the hardware debounce delay after the
most recent key release event.

Signed-off-by: David Collins <[e-mail]>
Signed-off-by: Anjelique Melendez <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/misc/pm8941-pwrkey.c

···
 #include <linux/input.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
+#include <linux/ktime.h>
 #include <linux/log2.h>
 #include <linux/module.h>
 #include <linux/of.h>
···
 #include <linux/regmap.h>
 
 #define PON_REV2			0x01
+
+#define PON_SUBTYPE			0x05
+
+#define PON_SUBTYPE_PRIMARY		0x01
+#define PON_SUBTYPE_SECONDARY		0x02
+#define PON_SUBTYPE_1REG		0x03
+#define PON_SUBTYPE_GEN2_PRIMARY	0x04
+#define PON_SUBTYPE_GEN2_SECONDARY	0x05
+#define PON_SUBTYPE_GEN3_PBS		0x08
+#define PON_SUBTYPE_GEN3_HLOS		0x09
 
 #define PON_RT_STS			0x10
 #define  PON_KPDPWR_N_SET		BIT(0)
···
 	struct input_dev *input;
 
 	unsigned int revision;
+	unsigned int subtype;
 	struct notifier_block reboot_notifier;
 
 	u32 code;
+	u32 sw_debounce_time_us;
+	ktime_t sw_debounce_end_time;
 	const struct pm8941_data *data;
 };
 
···
 {
 	struct pm8941_pwrkey *pwrkey = _data;
 	unsigned int sts;
-	int error;
+	int err;
 
-	error = regmap_read(pwrkey->regmap,
-			    pwrkey->baseaddr + PON_RT_STS, &sts);
-	if (error)
+	if (pwrkey->sw_debounce_time_us) {
+		if (ktime_before(ktime_get(), pwrkey->sw_debounce_end_time)) {
+			dev_dbg(pwrkey->dev,
+				"ignoring key event received before debounce end %llu us\n",
+				pwrkey->sw_debounce_end_time);
+			return IRQ_HANDLED;
+		}
+	}
+
+	err = regmap_read(pwrkey->regmap, pwrkey->baseaddr + PON_RT_STS, &sts);
+	if (err)
 		return IRQ_HANDLED;
 
-	input_report_key(pwrkey->input, pwrkey->code,
-			 sts & pwrkey->data->status_bit);
+	sts &= pwrkey->data->status_bit;
+
+	if (pwrkey->sw_debounce_time_us && !sts)
+		pwrkey->sw_debounce_end_time = ktime_add_us(ktime_get(),
+						pwrkey->sw_debounce_time_us);
+
+	input_report_key(pwrkey->input, pwrkey->code, sts);
 	input_sync(pwrkey->input);
 
 	return IRQ_HANDLED;
+}
+
+static int pm8941_pwrkey_sw_debounce_init(struct pm8941_pwrkey *pwrkey)
+{
+	unsigned int val, addr, mask;
+	int error;
+
+	if (pwrkey->data->has_pon_pbs && !pwrkey->pon_pbs_baseaddr) {
+		dev_err(pwrkey->dev,
+			"PON_PBS address missing, can't read HW debounce time\n");
+		return 0;
+	}
+
+	if (pwrkey->pon_pbs_baseaddr)
+		addr = pwrkey->pon_pbs_baseaddr + PON_DBC_CTL;
+	else
+		addr = pwrkey->baseaddr + PON_DBC_CTL;
+	error = regmap_read(pwrkey->regmap, addr, &val);
+	if (error)
+		return error;
+
+	if (pwrkey->subtype >= PON_SUBTYPE_GEN2_PRIMARY)
+		mask = 0xf;
+	else
+		mask = 0x7;
+
+	pwrkey->sw_debounce_time_us =
+		2 * USEC_PER_SEC / (1 << (mask - (val & mask)));
+
+	dev_dbg(pwrkey->dev, "SW debounce time = %u us\n",
+		pwrkey->sw_debounce_time_us);
+
+	return 0;
 }
 
 static int __maybe_unused pm8941_pwrkey_suspend(struct device *dev)
···
 		return error;
 	}
 
+	error = regmap_read(pwrkey->regmap, pwrkey->baseaddr + PON_SUBTYPE,
+			    &pwrkey->subtype);
+	if (error) {
+		dev_err(&pdev->dev, "failed to read subtype: %d\n", error);
+		return error;
+	}
+
 	error = of_property_read_u32(pdev->dev.of_node, "linux,code",
 				     &pwrkey->code);
 	if (error) {
···
 			return error;
 		}
 	}
+
+	error = pm8941_pwrkey_sw_debounce_init(pwrkey);
+	if (error)
+		return error;
 
 	if (pwrkey->data->pull_up_bit) {
 		error = regmap_update_bits(pwrkey->regmap,