ath11k: do not restore ASPM in case of single MSI vector

Current code enables ASPM by default, it allows MHI to enter M2 state.
In case of one MSI vector, system hang is observed if ath11k does MHI
register reading in this state. The issue was reported on Dell XPS 13
9310 but is seen also on XPS 15 and XPS 17 laptops.

The workaround here is to prevent MHI from entering M2 state, this can
be done by disabling ASPM if only one MSI vector is used. When using 32
vectors ASPM is enabled as before.

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1
Signed-off-by: NCarl Huang <cjhuang@codeaurora.org>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>
Signed-off-by: NBaochen Qiang <bqiang@codeaurora.org>
Link: https://lore.kernel.org/r/20211026041722.5271-1-bqiang@codeaurora.org

drivers/net/wireless/ath/ath11k/pci.c

@@ -1223,7 +1223,13 @@ static int ath11k_pci_start(struct ath11k_base *ab)
 
 	set_bit(ATH11K_PCI_FLAG_INIT_DONE, &ab_pci->flags);
 
-	ath11k_pci_aspm_restore(ab_pci);
+	/* TODO: for now don't restore ASPM in case of single MSI
+	 * vector as MHI register reading in M2 causes system hang.
+	 */
+	if (test_bit(ATH11K_PCI_FLAG_MULTI_MSI_VECTORS, &ab_pci->flags))
+		ath11k_pci_aspm_restore(ab_pci);
+	else
+		ath11k_info(ab, "leaving PCI ASPM disabled to avoid MHI M2 problems\n");
 
 	ath11k_pci_ce_irqs_enable(ab);
 	ath11k_ce_rx_post_buf(ab);