Bluetooth: btintel: Allow configuring drive strength of BRI

index 2ebc970e6573..cef74fd1271d 100644
@@ -12,6 +12,7 @@
 #include <linux/acpi.h>
 #include <acpi/acpi_bus.h>
 #include <asm/unaligned.h>
+#include <linux/efi.h>
 
 #include <net/bluetooth/bluetooth.h>
 #include <net/bluetooth/hci_core.h>

@@ -26,6 +27,8 @@
 #define ECDSA_OFFSET		644
 #define ECDSA_HEADER_LEN	320
 
+#define BTINTEL_EFI_DSBR	L"UefiCnvCommonDSBR"
+
 enum {
 	DSM_SET_WDISABLE2_DELAY = 1,
 	DSM_SET_RESET_METHOD = 3,

@@ -2616,6 +2619,120 @@ static u8 btintel_classify_pkt_type(struct hci_dev *hdev, struct sk_buff *skb)
 	return hci_skb_pkt_type(skb);
 }
 
+/*
+ * UefiCnvCommonDSBR UEFI variable provides information from the OEM platforms
+ * if they have replaced the BRI (Bluetooth Radio Interface) resistor to
+ * overcome the potential STEP errors on their designs. Based on the
+ * configauration, bluetooth firmware shall adjust the BRI response line drive
+ * strength. The below structure represents DSBR data.
+ * struct {
+ *	u8 header;
+ *	u32 dsbr;
+ * } __packed;
+ *
+ * header - defines revision number of the structure
+ * dsbr - defines drive strength BRI response
+ *	bit0
+ *		0 - instructs bluetooth firmware to use default values
+ *		1 - instructs bluetooth firmware to override default values
+ *	bit3:1
+ *		Reserved
+ *	bit7:4
+ *		DSBR override values (only if bit0 is set. Default value is 0xF
+ *	bit31:7
+ *		Reserved
+ * Expected values for dsbr field:
+ *	1. 0xF1 - indicates that the resistor on board is 33 Ohm
+ *	2. 0x00 or 0xB1 - indicates that the resistor on board is 10 Ohm
+ *	3. Non existing UEFI variable or invalid (none of the above) - indicates
+ *	   that the resistor on board is 10 Ohm
+ * Even if uefi variable is not present, driver shall send 0xfc0a command to
+ * firmware to use default values.
+ *
+ */
+static int btintel_uefi_get_dsbr(u32 *dsbr_var)
+{
+	struct btintel_dsbr {
+		u8 header;
+		u32 dsbr;
+	} __packed data;
+
+	efi_status_t status;
+	unsigned long data_size = 0;
+	efi_guid_t guid = EFI_GUID(0xe65d8884, 0xd4af, 0x4b20, 0x8d, 0x03,
+				   0x77, 0x2e, 0xcc, 0x3d, 0xa5, 0x31);
+
+	if (!IS_ENABLED(CONFIG_EFI))
+		return -EOPNOTSUPP;
+
+	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE))
+		return -EOPNOTSUPP;
+
+	status = efi.get_variable(BTINTEL_EFI_DSBR, &guid, NULL, &data_size,
+				  NULL);
+
+	if (status != EFI_BUFFER_TOO_SMALL || !data_size)
+		return -EIO;
+
+	status = efi.get_variable(BTINTEL_EFI_DSBR, &guid, NULL, &data_size,
+				  &data);
+
+	if (status != EFI_SUCCESS)
+		return -ENXIO;
+
+	*dsbr_var = data.dsbr;
+	return 0;
+}
+
+static int btintel_set_dsbr(struct hci_dev *hdev, struct intel_version_tlv *ver)
+{
+	struct btintel_dsbr_cmd {
+		u8 enable;
+		u8 dsbr;
+	} __packed;
+
+	struct btintel_dsbr_cmd cmd;
+	struct sk_buff *skb;
+	u8 status;
+	u32 dsbr;
+	bool apply_dsbr;
+	int err;
+
+	/* DSBR command needs to be sent for BlazarI + B0 step product after
+	 * downloading IML image.
+	 */
+	apply_dsbr = (ver->img_type == BTINTEL_IMG_IML &&
+		((ver->cnvi_top & 0xfff) == BTINTEL_CNVI_BLAZARI) &&
+		INTEL_CNVX_TOP_STEP(ver->cnvi_top) == 0x01);
+
+	if (!apply_dsbr)
+		return 0;
+
+	dsbr = 0;
+	err = btintel_uefi_get_dsbr(&dsbr);
+	if (err < 0)
+		bt_dev_dbg(hdev, "Error reading efi: %ls  (%d)",
+			   BTINTEL_EFI_DSBR, err);
+
+	cmd.enable = dsbr & BIT(0);
+	cmd.dsbr = dsbr >> 4 & 0xF;
+
+	bt_dev_info(hdev, "dsbr: enable: 0x%2.2x value: 0x%2.2x", cmd.enable,
+		    cmd.dsbr);
+
+	skb = __hci_cmd_sync(hdev, 0xfc0a, sizeof(cmd), &cmd,  HCI_CMD_TIMEOUT);
+	if (IS_ERR(skb))
+		return -bt_to_errno(PTR_ERR(skb));
+
+	status = skb->data[0];
+	kfree_skb(skb);
+
+	if (status)
+		return -bt_to_errno(status);
+
+	return 0;
+}
+
 int btintel_bootloader_setup_tlv(struct hci_dev *hdev,
 				 struct intel_version_tlv *ver)
 {

@@ -2650,6 +2767,13 @@ int btintel_bootloader_setup_tlv(struct hci_dev *hdev,
 	if (err)
 		return err;
 
+	/* set drive strength of BRI response */
+	err = btintel_set_dsbr(hdev, ver);
+	if (err) {
+		bt_dev_err(hdev, "Failed to send dsbr command (%d)", err);
+		return err;
+	}
+
 	/* If image type returned is BTINTEL_IMG_IML, then controller supports
 	 * intermediate loader image
 	 */