[PATCH v3 2/3] bus: mhi: host: Add a new API for getting channel doorbell address

[Qiang Yu]

Some controllers may want to know the address of a certain doorbell. Hence
add a new API where we read CHDBOFF register to get the base address of
doorbell, so that the controller can calculate the address of the doorbell
it wants by adding additional offset.

Signed-off-by: Qiang Yu <quic_qianyu@xxxxxxxxxxx>
---
 drivers/bus/mhi/host/main.c | 17 +++++++++++++++++
 include/linux/mhi.h         |  7 +++++++
 2 files changed, 24 insertions(+)

diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
index 15d657a..947b5ec 100644
--- a/drivers/bus/mhi/host/main.c
+++ b/drivers/bus/mhi/host/main.c
@@ -1691,3 +1691,20 @@ void mhi_unprepare_from_transfer(struct mhi_device *mhi_dev)
 	}
 }
 EXPORT_SYMBOL_GPL(mhi_unprepare_from_transfer);
+
+int mhi_get_channel_doorbell(struct mhi_controller *mhi_cntrl, u32 *chdb_offset)
+{
+	struct device *dev = &mhi_cntrl->mhi_dev->dev;
+	void __iomem *base = mhi_cntrl->regs;
+	int ret;
+
+	/* Read channel db offset */
+	ret = mhi_read_reg(mhi_cntrl, base, CHDBOFF, chdb_offset);
+	if (ret) {
+		dev_err(dev, "Unable to read CHDBOFF register\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mhi_get_channel_doorbell);
diff --git a/include/linux/mhi.h b/include/linux/mhi.h
index 8280545..1135142 100644
--- a/include/linux/mhi.h
+++ b/include/linux/mhi.h
@@ -816,4 +816,11 @@ int mhi_queue_skb(struct mhi_device *mhi_dev, enum dma_data_direction dir,
  */
 bool mhi_queue_is_full(struct mhi_device *mhi_dev, enum dma_data_direction dir);
 
+/**
+ * mhi_get_channel_doorbell - read channel doorbell offset register to get
+ *                            channel doorbell address
+ * @mhi_cntrl: MHI controller
+ * @chdb_offset: channel doorbell address
+ */
+int mhi_get_channel_doorbell(struct mhi_controller *mhi_cntrl, u32 *chdb_offset);
 #endif /* _MHI_H_ */
-- 
2.7.4