Question about iwl_pcie_rxq_inc_wr_ptr

I would like to ask if below change is safe (I'm considering to do that change on iwlegacy):

drivers/net/wireless/iwlwifi/pcie/rx.c +1 -1

index 567e67a..1ebdb83 100644
@@ -183,7 +183,7 @@ static void iwl_pcie_rxq_inc_wr_ptr(struct iwl_trans
 *trans, struct iwl_rxq *q)
 		} else {
 			/* Device expects a multiple of 8 */
 			q->write_actual = (q->write & ~0x7);
-			iwl_write_direct32(trans, FH_RSCSR_CHNL0_WPTR,
+			iwl_write32(trans, FH_RSCSR_CHNL0_WPTR,
 				q->write_actual);
 		}

}

This register seems to be only read by firmware, so maybe we can modify it without grab nic access. We are doing that on iwl_pcie_txq_inc_wr_ptr().

Quoted 20 lines

I would like to ask if below change is safe (I'm considering to do that change on iwlegacy):

drivers/net/wireless/iwlwifi/pcie/rx.c +1 -1

index 567e67a..1ebdb83 100644
@@ -183,7 +183,7 @@ static void iwl_pcie_rxq_inc_wr_ptr(struct iwl_trans
 *trans, struct iwl_rxq *q)
 		} else {
 			/* Device expects a multiple of 8 */
 			q->write_actual = (q->write & ~0x7);
-			iwl_write_direct32(trans, FH_RSCSR_CHNL0_WPTR,
+			iwl_write32(trans, FH_RSCSR_CHNL0_WPTR,
 				q->write_actual);
 		}

}

Quoted 3 lines

This register seems to be only read by firmware, so maybe we can modify it without grab nic access. We are doing that on iwl_pcie_txq_inc_wr_ptr().

I am not sure...
I am not sure what would be the behavior: not updating the value at all, or having the HW use an old value for a while. Does this cost you so much CPU that it justifies such a change?

Quoted 20 lines

Quoted 20 lines

I would like to ask if below change is safe (I'm considering to do that change on iwlegacy):

drivers/net/wireless/iwlwifi/pcie/rx.c +1 -1

index 567e67a..1ebdb83 100644
@@ -183,7 +183,7 @@ static void iwl_pcie_rxq_inc_wr_ptr(struct
 iwl_trans *trans, struct iwl_rxq *q)
 		} else {
 			/* Device expects a multiple of 8 */
 			q->write_actual = (q->write & ~0x7);
-			iwl_write_direct32(trans, FH_RSCSR_CHNL0_WPTR,
+			iwl_write32(trans, FH_RSCSR_CHNL0_WPTR,
 				q->write_actual);
 		}

}

Quoted 2 lines

Quoted 2 lines

This register seems to be only read by firmware, so maybe we can modify it without grab nic access. We are doing that on

iwl_pcie_txq_inc_wr_ptr().

Quoted 4 lines

Quoted 1 line

I am not sure...
I am not sure what would be the behavior: not updating the value at all, or

having the HW use an old value for a while.

Quoted 1 line

Does this cost you so much CPU that it justifies such a change?

I have those bug reports:

https://bugzilla.redhat.com/show_bug.cgi?id=863386
https://bugzilla.redhat.com/show_bug.cgi?id=889467
https://bugzilla.redhat.com/show_bug.cgi?id=895650
https://bugzilla.redhat.com/show_bug.cgi?id=989025

All are 4965 specific - I haven't seen similar traces on iwlwifi. On some cases use nohz=off boot option helped with the problem, so this could be also some kernel issue when udelay() is not working as expected. Anyway I'm considering to remove grab_nic_access from that path and would like to know possible consequences from firmware perspective.