[PATCH v2 3/3] Bluetooth: hci_bcm4377: keep ASPM off only while the firmware boots

[Andre Eikmeyer <dev@deq.rocks>]

The BCM4377 needs ASPM disabled because of a hardware erratum, and the
driver disables it on the whole link for as long as the device is bound.
On the MacBookAir9,1 this keeps the link to the Wi-Fi and Bluetooth chip
in L0, and the package does not go deeper than PC3.

Disable ASPM only in this function's Link Control register before the
function level reset and the firmware boot, and restore the saved value
once the firmware runs. A non-ARI Multi-Function Device enables only the
ASPM states enabled in all of its functions, so the link stays in L0
until then.

Tested on a MacBookAir9,1: with ASPM L1 enabled by the PCI core the link
returns to L1 after probe and after the re-probe that follows ACPI S3,
Bluetooth and Wi-Fi keep working, and the package reaches PC8 instead of
PC3 at idle.

Signed-off-by: Andre Eikmeyer <dev@deq.rocks>
---
 drivers/bluetooth/hci_bcm4377.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/drivers/bluetooth/hci_bcm4377.c b/drivers/bluetooth/hci_bcm4377.c
index 4e3630774c0..0d2103cfd9b 100644
--- a/drivers/bluetooth/hci_bcm4377.c
+++ b/drivers/bluetooth/hci_bcm4377.c
@@ -497,7 +497,8 @@ struct bcm4377_data;
  * clear_pciecfg_subsystem_ctrl_bit19: Set to true if bit 19 in the
  *                                     vendor-specific subsystem control
  *                                     register has to be cleared
- * disable_aspm: Set to true if ASPM must be disabled due to hardware errata
+ * disable_aspm: Set to true if ASPM must be disabled while the firmware is
+ *               loaded and booted due to hardware errata
  * broken_ext_scan: Set to true if the chip erroneously claims to support
  *                  extended scanning
  * broken_mws_transport_config: Set to true if the chip erroneously claims to
@@ -572,6 +573,9 @@ struct bcm4377_data {
 	/* set when the controller lost its firmware during system sleep */
 	bool fw_lost;
 
+	/* Link Control value saved while ASPM is disabled for the boot */
+	u16 link_ctl;
+
 	void __iomem *bar0;
 	void __iomem *bar2;
 
@@ -2260,20 +2264,27 @@ static int bcm4377_probe_of(struct bcm4377_data *bcm4377)
 	return 0;
 }
 
+/*
+ * ASPM is disabled in this function's Link Control register only. A
+ * non-ARI Multi-Function Device enables only the ASPM states enabled in
+ * all of its functions, so the link stays in L0 until it is restored.
+ */
 static void bcm4377_disable_aspm(struct bcm4377_data *bcm4377)
 {
-	pci_disable_link_state(bcm4377->pdev,
-			       PCIE_LINK_STATE_L0S | PCIE_LINK_STATE_L1);
-
-	/*
-	 * pci_disable_link_state can fail if either CONFIG_PCIEASPM is disabled
-	 * or if the BIOS hasn't handed over control to us. We must *always*
-	 * disable ASPM for this device due to hardware errata though.
-	 */
+	pcie_capability_read_word(bcm4377->pdev, PCI_EXP_LNKCTL,
+				  &bcm4377->link_ctl);
 	pcie_capability_clear_word(bcm4377->pdev, PCI_EXP_LNKCTL,
 				   PCI_EXP_LNKCTL_ASPMC);
 }
 
+static void bcm4377_restore_aspm(struct bcm4377_data *bcm4377)
+{
+	pcie_capability_clear_and_set_word(bcm4377->pdev, PCI_EXP_LNKCTL,
+					   PCI_EXP_LNKCTL_ASPMC,
+					   bcm4377->link_ctl &
+					   PCI_EXP_LNKCTL_ASPMC);
+}
+
 static void bcm4377_pci_free_irq_vectors(void *data)
 {
 	pci_free_irq_vectors(data);
@@ -2425,6 +2436,9 @@ static int bcm4377_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	if (ret)
 		return ret;
 
+	if (bcm4377->hw->disable_aspm)
+		bcm4377_restore_aspm(bcm4377);
+
 	ret = hci_register_dev(hdev);
 	if (ret < 0)
 		return ret;