netdev - [PATCH net v4 2/2] sfc: Restrict PIO to 64-bit architectures

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Message-ID: <538D9DD3.5030800@solarflare.com>
Date:	Tue, 3 Jun 2014 11:05:07 +0100
From:	Shradha Shah <sshah@...arflare.com>
To:	David Miller <davem@...emloft.net>
CC:	<netdev@...r.kernel.org>, <linux-net-drivers@...arflare.com>
Subject: [PATCH net v4 2/2] sfc: Restrict PIO to 64-bit architectures

From: Jon Cooper <jcooper@...arflare.com>

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

Fixes:ee45fd92c739
("sfc: Use TX PIO for sufficiently small packets")

Signed-off-by: Shradha Shah <sshah@...arflare.com>
---
 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
 #endif
 
+/* 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 */
 #ifdef ARCH_HAS_IOREMAP_WC
 #define EFX_USE_PIO 1
 #endif
+#endif
+#endif
 
 #ifdef EFX_USE_QWORD_IO
 static inline void _efx_writeq(struct efx_nic *efx, __le64 value,
--
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