sfc: Use rmb() to ensure reads occur in order

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@solarflare.com>

diff --git a/drivers/net/sfc/io.h b/drivers/net/sfc/io.h
index d9d8c2e..cc97880 100644 (file)
--- 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);