From: Jordan Crouse <jordan.crouse at amd.com>
This is a fix for the CS5535 errata 111:
When the SMBus controller tries to access a non-existing device, it sets
the NEGACK bit, SMBus I/O offset 01h[4], to 1 after it detects no
acknowledge at the ninth clock. The specification states that the bit
can be cleared by writing a 1 to it, but under certain circumstances it
is possible for this bit to not clear.
Writing a 0 to the bit resets the internal state machine and clears the
issue.
Since all writable bits in ACBST are W1C bits (write-one-to-clear) the
second write doesn't affect any other logic except the buggy NEGACK
state machine. The second write clears an internal register which is
responsible for "overwriting" the NEGACK bit in ACBST.
Signed-off-by: Jordan Crouse <jordan.crouse at amd.com>
Signed-off-by: Andrew Morton <akpm at osdl.org>
Signed-off-by: Jean Delvare <khali at linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>
---
drivers/i2c/busses/scx200_acb.c | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)
95563d343fec8d3e2f667c95230ac4ab7674b757
diff --git a/drivers/i2c/busses/scx200_acb.c b/drivers/i2c/busses/scx200_acb.c
index 42e4e00..a140e45 100644
--- a/drivers/i2c/busses/scx200_acb.c
+++ b/drivers/i2c/busses/scx200_acb.c
@@ -133,6 +133,9 @@ static void scx200_acb_machine(struct sc
outb(inb(ACBCTL1) | ACBCTL1_STOP, ACBCTL1);
outb(ACBST_STASTR | ACBST_NEGACK, ACBST);
+
+ /* Reset the status register */
+ outb(0, ACBST);
return;
}
@@ -228,6 +231,10 @@ static void scx200_acb_poll(struct scx20
timeout = jiffies + POLL_TIMEOUT;
while (time_before(jiffies, timeout)) {
status = inb(ACBST);
+
+ /* Reset the status register to avoid the hang */
+ outb(0, ACBST);
+
if ((status & (ACBST_SDAST|ACBST_BER|ACBST_NEGACK)) != 0) {
scx200_acb_machine(iface, status);
return;
--
1.3.2
