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Date:	Thu, 29 May 2014 11:20:50 +0100
From:	Shradha Shah <>
To:	David Miller <>
CC:	<>, <>
Subject: [PATCH net v3 2/2] sfc: Restrict PIO to 64-bit architectures

From: Jon Cooper <>

Enable PIO for x86_64 architecture only.
Not tested on platforms other than x86_64.

("sfc: Use TX PIO for sufficiently small packets")

Signed-off-by: Shradha Shah <>
 drivers/net/ethernet/sfc/io.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ethernet/sfc/io.h b/drivers/net/ethernet/sfc/io.h
index 4d3f119..adadcf0 100644
--- a/drivers/net/ethernet/sfc/io.h
+++ b/drivers/net/ethernet/sfc/io.h
@@ -66,10 +66,18 @@
 #define EFX_USE_QWORD_IO 1
+/* PIO only works on 64-bit architectures */
+#if BITS_PER_LONG == 64
+/* not strictly necessary to restrict to x86 arch, but done for safety
+ * since unusual write combining behaviour can break PIO.
+ */
+#ifdef CONFIG_X86_64
 /* PIO is a win only if write-combining is possible */
 #define EFX_USE_PIO 1
 static inline void _efx_writeq(struct efx_nic *efx, __le64 value,
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