linux-kernel - [PATCH 4.4 13/37] irda: fix overly long udelay()

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Message-Id: <20180605170109.686137201@linuxfoundation.org>
Date:   Tue,  5 Jun 2018 19:01:18 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>,
        Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 4.4 13/37] irda: fix overly long udelay()

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

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

From: Arnd Bergmann <arnd@...db.de>

commit c9bd28233b6d0d82ac3ba0215723be0a8262c39c upstream.

irda_get_mtt() returns a hardcoded '10000' in some cases,
and with gcc-7, we get a build error because this triggers a
compile-time check in udelay():

drivers/net/irda/w83977af_ir.o: In function `w83977af_hard_xmit':
w83977af_ir.c:(.text.w83977af_hard_xmit+0x14c): undefined reference to `__bad_udelay'

Older compilers did not run into this because they either did not
completely inline the irda_get_mtt() or did not consider the
10000 value a constant expression.

The code has been wrong since the start of git history.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: David S. Miller <davem@...emloft.net>
Cc: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/irda/w83977af_ir.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/irda/w83977af_ir.c
+++ b/drivers/net/irda/w83977af_ir.c
@@ -518,7 +518,9 @@ static netdev_tx_t w83977af_hard_xmit(st
 		
 		mtt = irda_get_mtt(skb);
 		pr_debug("%s(%ld), mtt=%d\n", __func__ , jiffies, mtt);
-			if (mtt)
+			if (mtt > 1000)
+				mdelay(mtt/1000);
+			else if (mtt)
 				udelay(mtt);
 
 			/* Enable DMA interrupt */