[RFC 3/4] iwlwifi: cleanup/fix memory barriers

[Stanislaw Gruszka <sgruszka@redhat.com>]

wmb(), rmb() are not needed when writel(), readl() are used as
accessors for MMIO. We use them indirectly via iowrite32(),
ioread32().

What is needed mmiowb(), for synchronizing writes coming from
different CPUs on PCIe bridge (see in patch comments). This
fortunately is not needed on x86, where mmiowb() is just
defined as compiler barrier. As iwlwifi devices are most likely
not used on anything other than x86, this is not so important
fix.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
---
 drivers/net/wireless/iwlwifi/iwl-agn.c           |    1 -
 drivers/net/wireless/iwlwifi/iwl-io.c            |   12 +++++++-----
 drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c |    1 -
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireless/iwlwifi/iwl-agn.c b/drivers/net/wireless/iwlwifi/iwl-agn.c
index 2642bf9..6636149 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn.c
@@ -336,7 +336,6 @@ static void iwl_print_cont_event_trace(struct iwl_priv *priv, u32 base,
 
 	/* Set starting address; reads will auto-increment */
 	iwl_write32(bus(priv), HBUS_TARG_MEM_RADDR, ptr);
-	rmb();
 
 	/*
 	 * Refuse to read more than would have fit into the log from
diff --git a/drivers/net/wireless/iwlwifi/iwl-io.c b/drivers/net/wireless/iwlwifi/iwl-io.c
index b5d0bcb..111182b 100644
--- a/drivers/net/wireless/iwlwifi/iwl-io.c
+++ b/drivers/net/wireless/iwlwifi/iwl-io.c
@@ -135,6 +135,13 @@ void iwl_release_nic_access(struct iwl_bus *bus)
 	lockdep_assert_held(&bus->reg_lock);
 	__iwl_clear_bit(bus, CSR_GP_CNTRL,
 			CSR_GP_CNTRL_REG_FLAG_MAC_ACCESS_REQ);
+	/*
+	 * In above we are reading CSR_GP_CNTRL register, what will flush any
+	 * previous writes, but still want to write, which clear MAC_ACCESS_REQ
+	 * bit, be performed on PCI bus, before any other writes scheduled on
+	 * different CPUs after we drop reg_lock.
+	 */
+	mmiowb();
 }
 
 u32 iwl_read_direct32(struct iwl_bus *bus, u32 reg)
@@ -181,7 +188,6 @@ int iwl_poll_direct_bit(struct iwl_bus *bus, u32 addr, u32 mask,
 static inline u32 __iwl_read_prph(struct iwl_bus *bus, u32 reg)
 {
 	iwl_write32(bus, HBUS_TARG_PRPH_RADDR, reg | (3 << 24));
-	rmb();
 	return iwl_read32(bus, HBUS_TARG_PRPH_RDAT);
 }
 
@@ -189,7 +195,6 @@ static inline void __iwl_write_prph(struct iwl_bus *bus, u32 addr, u32 val)
 {
 	iwl_write32(bus, HBUS_TARG_PRPH_WADDR,
 		    ((addr & 0x0000FFFF) | (3 << 24)));
-	wmb();
 	iwl_write32(bus, HBUS_TARG_PRPH_WDAT, val);
 }
 
@@ -268,7 +273,6 @@ void _iwl_read_targ_mem_words(struct iwl_bus *bus, u32 addr,
 	spin_lock_irqsave(&bus->reg_lock, flags);
 	if (likely(iwl_grab_nic_access(bus))) {
 		iwl_write32(bus, HBUS_TARG_MEM_RADDR, addr);
-		rmb();
 		for (offs = 0; offs < words; offs++)
 			vals[offs] = iwl_read32(bus, HBUS_TARG_MEM_RDAT);
 		iwl_release_nic_access(bus);
@@ -295,8 +299,6 @@ int _iwl_write_targ_mem_words(struct iwl_bus *bus, u32 addr,
 	spin_lock_irqsave(&bus->reg_lock, flags);
 	if (likely(iwl_grab_nic_access(bus))) {
 		iwl_write32(bus, HBUS_TARG_MEM_WADDR, addr);
-		wmb();
-
 		for (offs = 0; offs < words; offs++)
 			iwl_write32(bus, HBUS_TARG_MEM_WDAT, vals[offs]);
 		iwl_release_nic_access(bus);
diff --git a/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c b/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
index 7b7899d..3564b86 100644
--- a/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-trans-pcie-rx.c
@@ -747,7 +747,6 @@ static int iwl_print_event_log(struct iwl_trans *trans, u32 start_idx,
 
 	/* Set starting address; reads will auto-increment */
 	iwl_write32(bus(trans), HBUS_TARG_MEM_RADDR, ptr);
-	rmb();
 
 	/* "time" is actually "data" for mode 0 (no timestamp).
 	* place event id # at far right for easier visual parsing. */
-- 
1.7.1