[PATCH v2 1/5] phy: cpcap-usb: Prevent line glitches from triggering sysrq

We can get random sysrq events on switching from USB to debug serial
port mode unless we temporarily disable sysrq on serial line for the mode
changes.

Suggested-by: Tony Lindgren <[email protected]>
Signed-off-by: Ivaylo Dimitrov <[email protected]>
---
 drivers/phy/motorola/phy-cpcap-usb.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/phy/motorola/phy-cpcap-usb.c b/drivers/phy/motorola/phy-cpcap-usb.c
index 7cb020dd3423..d1c70c715346 100644
--- a/drivers/phy/motorola/phy-cpcap-usb.c
+++ b/drivers/phy/motorola/phy-cpcap-usb.c
@@ -20,6 +20,7 @@
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
 #include <linux/slab.h>
+#include <linux/sysrq.h>
 
 #include <linux/gpio/consumer.h>
 #include <linux/mfd/motorola-cpcap.h>
@@ -413,7 +414,12 @@ static int cpcap_usb_gpio_set_mode(struct cpcap_phy_ddata *ddata,
 
 static int cpcap_usb_set_uart_mode(struct cpcap_phy_ddata *ddata)
 {
-	int error;
+	int old_sysrq_mask, error;
+
+	/* Disable sysrq to prevent random sysrq events on line glitches */
+	old_sysrq_mask = sysrq_mask();
+	if (old_sysrq_mask & 1)
+		sysrq_toggle_support(old_sysrq_mask & ~1);
 
 	/* Disable lines to prevent glitches from waking up mdm6600 */
 	error = cpcap_usb_gpio_set_mode(ddata, CPCAP_UNKNOWN_DISABLED);
@@ -445,13 +451,13 @@ static int cpcap_usb_set_uart_mode(struct cpcap_phy_ddata *ddata)
 
 	/* Enable UART mode */
 	error = cpcap_usb_gpio_set_mode(ddata, CPCAP_DM_DP);
-	if (error)
-		goto out_err;
-
-	return 0;
 
 out_err:
-	dev_err(ddata->dev, "%s failed with %i\n", __func__, error);
+	if (old_sysrq_mask & 1)
+		sysrq_toggle_support(old_sysrq_mask);
+
+	if (error)
+		dev_err(ddata->dev, "%s failed with %i\n", __func__, error);
 
 	return error;
 }
-- 
2.39.5