@@ -200,6 +200,26 @@ static inline int _iwl_grab_nic_access(struct iwl_priv *priv)
/* this bit wakes up the NIC */
_iwl_set_bit(priv, CSR_GP_CNTRL, CSR_GP_CNTRL_REG_FLAG_MAC_ACCESS_REQ);
+
+ /*
+ * These bits say the device is running, and should keep running for
+ * at least a short while (at least as long as MAC_ACCESS_REQ stays 1),
+ * but they do not indicate that embedded SRAM is restored yet;
+ * 3945 and 4965 have volatile SRAM, and must save/restore contents
+ * to/from host DRAM when sleeping/waking for power-saving.
+ * Each direction takes approximately 1/4 millisecond; with this
+ * overhead, it's a good idea to grab and hold MAC_ACCESS_REQUEST if a
+ * series of register accesses are expected (e.g. reading Event Log),
+ * to keep device from sleeping.
+ *
+ * CSR_UCODE_DRV_GP1 register bit MAC_SLEEP == 0 indicates that
+ * SRAM is okay/restored. We don't check that here because this call
+ * is just for hardware register access; but GP1 MAC_SLEEP check is a
+ * good idea before accessing 3945/4965 SRAM (e.g. reading Event Log).
+ *
+ * 5000 series and later (including 1000 series) have non-volatile SRAM,
+ * and do not save/restore SRAM when power cycling.
+ */
ret = _iwl_poll_bit(priv, CSR_GP_CNTRL,
CSR_GP_CNTRL_REG_VAL_MAC_ACCESS_EN,
(CSR_GP_CNTRL_REG_FLAG_MAC_CLOCK_READY |