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
--- a/drivers/net/sfc/io.h
+++ b/drivers/net/sfc/io.h
@@ -152,6 +152,7 @@
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 @@
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);