[coreboot-gerrit] Change in coreboot[master]: device/software_i2c: Add function to recover bus

[Patrick Rudolph (Code Review)]

Patrick Rudolph has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/35725 )

Change subject: device/software_i2c: Add function to recover bus
......................................................................

device/software_i2c: Add function to recover bus

As the software bus might be in unknown state, add a function to reset
it to known (idle) state.

Copied from linux kernel.
Tested on Supermicro X11SSH-TF.

Change-Id: I264471e872cb353b28a6b71cc64a11aec59e63f2
Signed-off-by: Patrick Rudolph 
---
M src/device/software_i2c.c
M src/include/device/i2c_simple.h
2 files changed, 48 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/25/35725/1

diff --git a/src/device/software_i2c.c b/src/device/software_i2c.c
index 5dc9990..eecb670 100644
--- a/src/device/software_i2c.c
+++ b/src/device/software_i2c.c
@@ -343,3 +343,49 @@
    	"SDA %d, SCL %d\n", bus, bits, software_i2c[bus]->get_sda(bus),
    	software_i2c[bus]->get_scl(bus));
 }
+
+/*
+ * Try to recover the bus from unknown state.
+ * Useful if the power rail or reset line isn't under firmware control.
+ */
+#define RECOVERY_CLK_CNT	9
+
+int i2c_recover_bus(unsigned bus)
+{
+	int i = 0, scl = 1;
+
+	printk(BIOS_INFO, "software_i2c(%d): Trying i2c bus recovery\n", bus);
+
+	/*
+	 * If we can set SDA, we will always create a STOP to ensure additional
+	 * pulses will do no harm. This is achieved by letting SDA follow SCL
+	 * half a cycle later. Check the 'incomplete_write_byte' fault injector
+	 * for details.
+	 */
+	software_i2c[bus]->set_scl(bus, 1);
+	wait(bus);
+	software_i2c[bus]->set_sda(bus, 1);
+	wait(bus);
+
+	/*
+	 * By this time SCL is high, as we need to give 9 falling-rising edges
+	 */
+	while (i++ < RECOVERY_CLK_CNT * 2) {
+		if (scl) {
+			/* SCL shouldn't be low here */
+			if (!software_i2c[bus]->get_scl(bus)) {
+				printk(BIOS_ERR, "software_i2c(%d): SCL stuck low\n", bus);
+				return 1;
+				break;
+			}
+		}
+
+		scl = !scl;
+		software_i2c[bus]->set_scl(bus, scl);
+		/* Creating STOP again, see above */
+		wait(bus);
+		software_i2c[bus]->set_sda(bus, scl);
+		wait(bus);
+	}
+	return 0;
+}
diff --git a/src/include/device/i2c_simple.h b/src/include/device/i2c_simple.h
index e3cc892..7f508b2 100644
--- a/src/include/device/i2c_simple.h
+++ b/src/include/device/i2c_simple.h
@@ -45,6 +45,8 @@
 int i2c_write_field(unsigned int bus, uint8_t slave, uint8_t reg, uint8_t data,
    	    uint8_t mask, uint8_t shift);

+int i2c_recover_bus(unsigned int bus);
+
 /*
  * software_i2c is supposed to be a debug feature. It's usually not compiled in,
  * but when it is it can be dynamically enabled at runtime for certain busses.