[PATCH v2 21/23] bus: mhi: ep: Add support for queueing SKBs over MHI bus

[Manivannan Sadhasivam]

Add support for queueing SKBs over MHI bus in the MHI endpoint stack.
The mhi_ep_queue_skb() API will be used by the client networking drivers
to queue the SKBs to the host over MHI.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
---
 drivers/bus/mhi/ep/main.c | 102 ++++++++++++++++++++++++++++++++++++++
 include/linux/mhi_ep.h    |  13 +++++
 2 files changed, 115 insertions(+)

diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
index c46d09cc67f4..8a8e90887060 100644
--- a/drivers/bus/mhi/ep/main.c
+++ b/drivers/bus/mhi/ep/main.c
@@ -488,6 +488,108 @@ int mhi_ep_process_tre_ring(struct mhi_ep_ring *ring, struct mhi_ep_ring_element
 	return 0;
 }
 
+int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, enum dma_data_direction dir,
+		     struct sk_buff *skb, size_t len, enum mhi_flags mflags)
+{
+	struct mhi_ep_chan *mhi_chan = (dir == DMA_FROM_DEVICE) ? mhi_dev->dl_chan :
+								mhi_dev->ul_chan;
+	struct mhi_ep_cntrl *mhi_cntrl = mhi_dev->mhi_cntrl;
+	struct device *dev = &mhi_chan->mhi_dev->dev;
+	struct mhi_ep_ring_element *el;
+	struct mhi_ep_ring *ring;
+	size_t bytes_to_write;
+	enum mhi_ev_ccs code;
+	void *read_from_loc;
+	u32 buf_remaining;
+	u64 write_to_loc;
+	u32 tre_len;
+	int ret = 0;
+
+	if (dir == DMA_TO_DEVICE)
+		return -EINVAL;
+
+	buf_remaining = len;
+	ring = &mhi_cntrl->mhi_chan[mhi_chan->chan].ring;
+
+	mutex_lock(&mhi_chan->lock);
+
+	do {
+		/* Don't process the transfer ring if the channel is not in RUNNING state */
+		if (mhi_chan->state != MHI_CH_STATE_RUNNING) {
+			dev_err(dev, "Channel not available");
+			ret = -ENODEV;
+			goto err_exit;
+		}
+
+		if (mhi_ep_queue_is_empty(mhi_dev, dir)) {
+			dev_err(dev, "TRE not available!\n");
+			ret = -EINVAL;
+			goto err_exit;
+		}
+
+		el = &ring->ring_cache[ring->rd_offset];
+		tre_len = MHI_EP_TRE_GET_LEN(el);
+		if (skb->len > tre_len) {
+			dev_err(dev, "Buffer size (%d) is too large for TRE (%d)!\n",
+				skb->len, tre_len);
+			ret = -ENOMEM;
+			goto err_exit;
+		}
+
+		bytes_to_write = min(buf_remaining, tre_len);
+		read_from_loc = skb->data;
+		write_to_loc = MHI_EP_TRE_GET_PTR(el);
+
+		ret = mhi_cntrl->write_to_host(mhi_cntrl, read_from_loc, write_to_loc,
+					       bytes_to_write);
+		if (ret < 0)
+			return ret;
+
+		buf_remaining -= bytes_to_write;
+		/*
+		 * For all TREs queued by the host for DL channel, only the EOT flag will be set.
+		 * If the packet doesn't fit into a single TRE, send the OVERFLOW event to
+		 * the host so that the host can adjust the packet boundary to next TREs. Else send
+		 * the EOT event to the host indicating the packet boundary.
+		 */
+		if (buf_remaining)
+			code = MHI_EV_CC_OVERFLOW;
+		else
+			code = MHI_EV_CC_EOT;
+
+		ret = mhi_ep_send_completion_event(mhi_cntrl, ring, bytes_to_write, code);
+		if (ret) {
+			dev_err(dev, "Error sending completion event");
+			goto err_exit;
+		}
+
+		mhi_ep_ring_inc_index(ring);
+	} while (buf_remaining);
+
+	/*
+	 * During high network traffic, sometimes the DL doorbell interrupt from the host is missed
+	 * by the endpoint. So manually check for the write pointer update here so that we don't run
+	 * out of buffer due to missing interrupts.
+	 */
+	if (ring->rd_offset + 1 == ring->wr_offset) {
+		ret = mhi_ep_update_wr_offset(ring);
+		if (ret) {
+			dev_err(dev, "Error updating write pointer\n");
+			goto err_exit;
+		}
+	}
+
+	mutex_unlock(&mhi_chan->lock);
+
+	return 0;
+
+err_exit:
+	mutex_unlock(&mhi_chan->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mhi_ep_queue_skb);
+
 static int mhi_ep_cache_host_cfg(struct mhi_ep_cntrl *mhi_cntrl)
 {
 	struct device *dev = &mhi_cntrl->mhi_dev->dev;
diff --git a/include/linux/mhi_ep.h b/include/linux/mhi_ep.h
index aaf4b6942037..75cfbf0c6fb0 100644
--- a/include/linux/mhi_ep.h
+++ b/include/linux/mhi_ep.h
@@ -277,4 +277,17 @@ void mhi_ep_power_down(struct mhi_ep_cntrl *mhi_cntrl);
  */
 bool mhi_ep_queue_is_empty(struct mhi_ep_device *mhi_dev, enum dma_data_direction dir);
 
+/**
+ * mhi_ep_queue_skb - Send SKBs to host over MHI Endpoint
+ * @mhi_dev: Device associated with the channels
+ * @dir: DMA direction for the channel
+ * @skb: Buffer for holding SKBs
+ * @len: Buffer length
+ * @mflags: MHI Endpoint transfer flags used for the transfer
+ *
+ * Return: 0 if the SKBs has been sent successfully, a negative error code otherwise.
+ */
+int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, enum dma_data_direction dir,
+		     struct sk_buff *skb, size_t len, enum mhi_flags mflags);
+
 #endif
-- 
2.25.1