From khali@linux-fr.org Fri Apr 28 13:53:26 2006 Date: Fri, 28 Apr 2006 22:53:30 +0200 From: Jean Delvare To: Greg KH Cc: Jordan Crouse Subject: [PATCH] scx200_acb: Fix for the CS5535 errata Message-Id: <20060428225330.8f95903f.khali@linux-fr.org> Content-Disposition: inline; filename=i2c-scx200_acb-fix-for-cs5535-errata.patch From: Jordan Crouse 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 Signed-off-by: Andrew Morton Signed-off-by: Jean Delvare Signed-off-by: Greg Kroah-Hartman --- drivers/i2c/busses/scx200_acb.c | 7 +++++++ 1 file changed, 7 insertions(+) --- gregkh-2.6.orig/drivers/i2c/busses/scx200_acb.c +++ gregkh-2.6/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;