Patch "w1:omap_hdq: fix regression" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    w1:omap_hdq: fix regression

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     w1-omap_hdq-fix-regression.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From ecfaf0c42fc4306b5ec4bf6be01b66f8fe9a9733 Mon Sep 17 00:00:00 2001
From: "H. Nikolaus Schaller" <hns@goldelico.com>
Date: Tue, 2 Aug 2016 14:07:12 -0700
Subject: w1:omap_hdq: fix regression

From: H. Nikolaus Schaller <hns@goldelico.com>

commit ecfaf0c42fc4306b5ec4bf6be01b66f8fe9a9733 upstream.

Commit e93762bbf681 ("w1: masters: omap_hdq: add support for 1-wire
mode") added a statement to clear the hdq_irqstatus flags in
hdq_read_byte().

If the hdq reading process is scheduled slowly or interrupts are
disabled for a while the hardware read activity might already be
finished on entry of hdq_read_byte().  And hdq_isr() already has set the
hdq_irqstatus to 0x6 (can be seen in debug mode) denoting that both, the
TXCOMPLETE and RXCOMPLETE interrupts occurred in parallel.

This means there is no need to wait and the hdq_read_byte() can just
read the byte from the hdq controller.

By resetting hdq_irqstatus to 0 the read process is forced to be always
waiting again (because the if statement always succeeds) but the
hardware will not issue another RXCOMPLETE interrupt.  This results in a
false timeout.

After such a situation the hdq bus hangs.

Link: http://lkml.kernel.org/r/b724765f87ad276a69625bc19806c8c8844c4590.1469513669.git.hns@goldelico.com
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/w1/masters/omap_hdq.c |    2 --
 1 file changed, 2 deletions(-)

--- a/drivers/w1/masters/omap_hdq.c
+++ b/drivers/w1/masters/omap_hdq.c
@@ -390,8 +390,6 @@ static int hdq_read_byte(struct hdq_data
 		goto out;
 	}
 
-	hdq_data->hdq_irqstatus = 0;
-
 	if (!(hdq_data->hdq_irqstatus & OMAP_HDQ_INT_STATUS_RXCOMPLETE)) {
 		hdq_reg_merge(hdq_data, OMAP_HDQ_CTRL_STATUS,
 			OMAP_HDQ_CTRL_STATUS_DIR | OMAP_HDQ_CTRL_STATUS_GO,


Patches currently in stable-queue which might be from hns@goldelico.com are

queue-4.4/w1-omap_hdq-fix-regression.patch