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

[Ivaylo Dimitrov]

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 <tony at atomide.com>
Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75 at gmail.com>
---
 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