netdev - [PATCH net-2.6 3/3] sfc: Use rmb() to ensure reads occur in order

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Message-ID: <1302652234.2880.31.camel@bwh-desktop>
Date:	Wed, 13 Apr 2011 00:50:34 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-net-drivers@...arflare.com
Subject: [PATCH net-2.6 3/3] sfc: Use rmb() to ensure reads occur in order

From: Neil Turton <nturton@...arflare.com>

Enabling write-combining may also enable read reordering.  The BIU is
only guaranteed to read from a 128-bit CSR or 64-bit SRAM word when
the host reads from its lowest address; otherwise the BIU may use the
latched value.  Therefore we need to reinstate the read memory
barriers after the first read operation for each CSR or SRAM word.

Signed-off-by; Ben Hutchings <bhutchings@...arflare.com>
---
 drivers/net/sfc/io.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/net/sfc/io.h b/drivers/net/sfc/io.h
index d9d8c2e..cc97880 100644
--- a/drivers/net/sfc/io.h
+++ b/drivers/net/sfc/io.h
@@ -152,6 +152,7 @@ static inline void efx_reado(struct efx_nic *efx, efx_oword_t *value,
 
 	spin_lock_irqsave(&efx->biu_lock, flags);
 	value->u32[0] = _efx_readd(efx, reg + 0);
+	rmb();
 	value->u32[1] = _efx_readd(efx, reg + 4);
 	value->u32[2] = _efx_readd(efx, reg + 8);
 	value->u32[3] = _efx_readd(efx, reg + 12);
@@ -174,6 +175,7 @@ static inline void efx_sram_readq(struct efx_nic *efx, void __iomem *membase,
 	value->u64[0] = (__force __le64)__raw_readq(membase + addr);
 #else
 	value->u32[0] = (__force __le32)__raw_readl(membase + addr);
+	rmb();
 	value->u32[1] = (__force __le32)__raw_readl(membase + addr + 4);
 #endif
 	spin_unlock_irqrestore(&efx->biu_lock, flags);
-- 
1.7.4


-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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