From 95563d343fec8d3e2f667c95230ac4ab7674b757 Mon Sep 17 00:00:00 2001 From: Jordan Crouse Date: Fri, 28 Apr 2006 22:53:30 +0200 Subject: [PATCH] scx200_acb: Fix for the CS5535 errata 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(+) (limited to 'drivers/i2c') diff --git a/drivers/i2c/busses/scx200_acb.c b/drivers/i2c/busses/scx200_acb.c index 42e4e00d6c32..a140e4536a4e 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 scx200_acb_iface *iface, u8 status) 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 scx200_acb_iface *iface) 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; -- cgit v1.2.3