linux-kernel - [ 08/84] drivers/scsi/atp870u.c: fix bad use of udelay

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Date:	Thu, 11 Oct 2012 11:02:52 +0900
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Martin Michlmayr <tbm@...ius.com>,
	Jonathan Nieder <jrnieder@...il.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 08/84] drivers/scsi/atp870u.c: fix bad use of udelay

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Michlmayr <tbm@...ius.com>

commit 0f6d93aa9d96cc9022b51bd10d462b03296be146 upstream.

The ACARD driver calls udelay() with a value > 2000, which leads to to
the following compilation error on ARM:

  ERROR: "__bad_udelay" [drivers/scsi/atp870u.ko] undefined!
  make[1]: *** [__modpost] Error 1

This is because udelay is defined on ARM, roughly speaking, as

	#define udelay(n) ((n) > 2000 ? __bad_udelay() : \
		__const_udelay((n) * ((2199023U*HZ)>>11)))

The argument to __const_udelay is the number of jiffies to wait divided
by 4, but this does not work unless the multiplication does not
overflow, and that is what the build error is designed to prevent.  The
intended behavior can be achieved by using mdelay to call udelay
multiple times in a loop.

[jrnieder@...il.com: adding context]
Signed-off-by: Martin Michlmayr <tbm@...ius.com>
Signed-off-by: Jonathan Nieder <jrnieder@...il.com>
Cc: James Bottomley <James.Bottomley@...senPartnership.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/scsi/atp870u.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/drivers/scsi/atp870u.c
+++ b/drivers/scsi/atp870u.c
@@ -1174,7 +1174,16 @@ wait_io1:
 	outw(val, tmport);
 	outb(2, 0x80);
 TCM_SYNC:
-	udelay(0x800);
+	/*
+	 * The funny division into multiple delays is to accomodate
+	 * arches like ARM where udelay() multiplies its argument by
+	 * a large number to initialize a loop counter.  To avoid
+	 * overflow, the maximum supported udelay is 2000 microseconds.
+	 *
+	 * XXX it would be more polite to find a way to use msleep()
+	 */
+	mdelay(2);
+	udelay(48);
 	if ((inb(tmport) & 0x80) == 0x00) {	/* bsy ? */
 		outw(0, tmport--);
 		outb(0, tmport);


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