[PATCH v2 3/6] bus: mhi: core: Add support to stop or start channel data transfers

[Bhaumik Bhatt]

Some MHI client drivers may want to request a pause or halt of
data transfer activity on their channels. Support for this does
not exist and must be introduced, wherein the channel context is
not reset or cleared but only the STOP channel command is issued.
This would need to be paired with an API that allows resuming the
data transfer activity on channels by use of the START channel
command. This API assumes that the context information is already
setup. Enable this using two new APIs, mhi_start_transfer() and
mhi_stop_transfer().

Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
---
 drivers/bus/mhi/core/main.c | 41 +++++++++++++++++++++++++++++++++++++++++
 include/linux/mhi.h         | 19 +++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
index 1226933..1a969f4 100644
--- a/drivers/bus/mhi/core/main.c
+++ b/drivers/bus/mhi/core/main.c
@@ -1560,6 +1560,47 @@ void mhi_unprepare_from_transfer(struct mhi_device *mhi_dev)
 }
 EXPORT_SYMBOL_GPL(mhi_unprepare_from_transfer);
 
+static int mhi_update_transfer_state(struct mhi_device *mhi_dev,
+				     enum mhi_ch_state_type to_state)
+{
+	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
+	struct mhi_chan *mhi_chan;
+	int dir, ret;
+
+	for (dir = 0; dir < 2; dir++) {
+		mhi_chan = dir ? mhi_dev->ul_chan : mhi_dev->dl_chan;
+
+		if (!mhi_chan)
+			continue;
+
+		/*
+		 * Bail out if one of the channels fail as client will reset
+		 * both upon failure
+		 */
+		mutex_lock(&mhi_chan->mutex);
+		ret = mhi_update_channel_state(mhi_cntrl, mhi_chan, to_state);
+		if (ret) {
+			mutex_unlock(&mhi_chan->mutex);
+			return ret;
+		}
+		mutex_unlock(&mhi_chan->mutex);
+	}
+
+	return 0;
+}
+
+int mhi_stop_transfer(struct mhi_device *mhi_dev)
+{
+	return mhi_update_transfer_state(mhi_dev, MHI_CH_STATE_TYPE_STOP);
+}
+EXPORT_SYMBOL_GPL(mhi_stop_transfer);
+
+int mhi_start_transfer(struct mhi_device *mhi_dev)
+{
+	return mhi_update_transfer_state(mhi_dev, MHI_CH_STATE_TYPE_START);
+}
+EXPORT_SYMBOL_GPL(mhi_start_transfer);
+
 int mhi_poll(struct mhi_device *mhi_dev, u32 budget)
 {
 	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
diff --git a/include/linux/mhi.h b/include/linux/mhi.h
index 52b3c60..aee8494 100644
--- a/include/linux/mhi.h
+++ b/include/linux/mhi.h
@@ -702,6 +702,25 @@ int mhi_prepare_for_transfer(struct mhi_device *mhi_dev);
 void mhi_unprepare_from_transfer(struct mhi_device *mhi_dev);
 
 /**
+ * mhi_stop_transfer - Pauses ongoing channel activity by issuing the STOP
+ *                     channel command to both UL and DL channels. This command
+ *                     does not reset the channel context and the client drivers
+ *                     can issue mhi_start_transfer to resume activity.
+ * @mhi_dev: Device associated with the channels
+ */
+int mhi_stop_transfer(struct mhi_device *mhi_dev);
+
+/**
+ * mhi_start_transfer - Resumes channel activity by issuing the START channel
+ *                      command to both UL and DL channels. This command assumes
+ *                      the channel context is already setup and the client
+ *                      drivers can issue mhi_stop_transfer to pause activity if
+ *                      required.
+ * @mhi_dev: Device associated with the channels
+ */
+int mhi_start_transfer(struct mhi_device *mhi_dev);
+
+/**
  * mhi_poll - Poll for any available data in DL direction
  * @mhi_dev: Device associated with the channels
  * @budget: # of events to process
-- 
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