[PATCH AUTOSEL 6.18-6.12] Bluetooth: btintel_pcie: Add 50 ms delay before MAC init on BlazarIW

[Sasha Levin <sashal@kernel.org>]

From: Kiran K <kiran.k@intel.com>

[ Upstream commit 4d62d88e7ae6dcecd9a8c70a045a6c6c64bf3b52 ]

On BlazarIW, fast restart cycles fail because the D0 entry to MAC
init does not complete in time. As a result, MAC initialization
does not proceed and the controller fails to transition past the
ROM boot stage.

Add a 50 ms delay (worst case as per HW analysis) before doing MAC
init in btintel_pcie_enable_bt() so the shared hardware reset flow
has time to complete. The delay is gated on the BlazarIW PCI device
id 0x4D76 so other Intel BT PCIe controllers are unaffected.

Signed-off-by: Kiran K <kiran.k@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The background checks finished and match the earlier analysis:

1. **Commit search** — The BlazarIW 50 ms delay patch is **not in this
   local tree**. A `git log --grep="50 ms delay"` only turned up
   unrelated delay commits in other subsystems (xprtrdma, hci_qca, drm).

2. **BlazarIW support** — Device `0x4D76` landed via `6053b532d345b` and
   is present from the **v6.17/v6.18** era onward. It is **not** in
   v6.12, which fits evaluating this only for the checked-out
   **v6.18.44** tree.

That leaves the conclusion unchanged: backport **YES** for this tree —
BlazarIW is supported here, but the MAC-init timing fix is still
missing.

 drivers/bluetooth/btintel_pcie.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/bluetooth/btintel_pcie.c b/drivers/bluetooth/btintel_pcie.c
index d0aa1666d6ac6..c0441541c0862 100644
--- a/drivers/bluetooth/btintel_pcie.c
+++ b/drivers/bluetooth/btintel_pcie.c
@@ -740,6 +740,11 @@ static void btintel_pcie_dump_traces(struct hci_dev *hdev)
 		bt_dev_err(hdev, "Failed to dump traces: (%d)", ret);
 }
 
+static bool btintel_pcie_is_blazariw(struct pci_dev *pdev)
+{
+	return pdev->device == 0x4D76;
+}
+
 /* This function enables BT function by setting BTINTEL_PCIE_CSR_FUNC_CTRL_MAC_INIT bit in
  * BTINTEL_PCIE_CSR_FUNC_CTRL_REG register and wait for MSI-X with
  * BTINTEL_PCIE_MSIX_HW_INT_CAUSES_GP0.
@@ -759,6 +764,14 @@ static int btintel_pcie_enable_bt(struct btintel_pcie_data *data)
 	btintel_pcie_wr_reg32(data, BTINTEL_PCIE_CSR_CI_ADDR_MSB_REG,
 			      (u64)data->ci_p_addr >> 32);
 
+	/* On BlazarIW, the D0 entry to MAC init does not complete in
+	 * time. Wait 50 ms (worst case as per HW analysis) for the
+	 * shared hardware reset flow to complete before proceeding with
+	 * MAC init.
+	 */
+	if (btintel_pcie_is_blazariw(data->pdev))
+		msleep(50);
+
 	/* Reset the cached value of boot stage. it is updated by the MSI-X
 	 * gp0 interrupt handler.
 	 */
-- 
2.53.0