mei: dma ring: implement rx circular buffer logic

Implement circular buffer protocol over receive dma
buffer. Add extension to the mei message header that holds
length of the buffer on the dma buffer.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 61 insertions, 0 deletions

diff --git a/drivers/misc/mei/dma-ring.c b/drivers/misc/mei/dma-ring.c
index b73d5ab54070..a0c40925049a 100644
--- a/drivers/misc/mei/dma-ring.c
+++ b/drivers/misc/mei/dma-ring.c
@@ -117,3 +117,64 @@ void mei_dma_ring_reset(struct mei_device *dev)
 
 	memset(ctrl, 0, sizeof(*ctrl));
 }
+
+/**
+ * mei_dma_copy_from() - copy from dma ring into buffer
+ * @dev: mei device
+ * @buf: data buffer
+ * @offset: offset in slots.
+ * @n: number of slots to copy.
+ */
+static size_t mei_dma_copy_from(struct mei_device *dev, unsigned char *buf,
+				u32 offset, u32 n)
+{
+	unsigned char *dbuf = dev->dr_dscr[DMA_DSCR_DEVICE].vaddr;
+
+	size_t b_offset = offset << 2;
+	size_t b_n = n << 2;
+
+	memcpy(buf, dbuf + b_offset, b_n);
+
+	return b_n;
+}
+
+/**
+ * mei_dma_ring_read() - read data from the ring
+ * @dev: mei device
+ * @buf: buffer to read into: may be NULL in case of droping the data.
+ * @len: length to read.
+ */
+void mei_dma_ring_read(struct mei_device *dev, unsigned char *buf, u32 len)
+{
+	struct hbm_dma_ring_ctrl *ctrl = mei_dma_ring_ctrl(dev);
+	u32 dbuf_depth;
+	u32 rd_idx, rem, slots;
+
+	if (WARN_ON(!ctrl))
+		return;
+
+	dev_dbg(dev->dev, "reading from dma %u bytes\n", len);
+
+	if (!len)
+		return;
+
+	dbuf_depth = dev->dr_dscr[DMA_DSCR_DEVICE].size >> 2;
+	rd_idx = READ_ONCE(ctrl->dbuf_rd_idx) & (dbuf_depth - 1);
+	slots = mei_data2slots(len);
+
+	/* if buf is NULL we drop the packet by advancing the pointer.*/
+	if (!buf)
+		goto out;
+
+	if (rd_idx + slots > dbuf_depth) {
+		buf += mei_dma_copy_from(dev, buf, rd_idx, dbuf_depth - rd_idx);
+		rem = slots - (dbuf_depth - rd_idx);
+		rd_idx = 0;
+	} else {
+		rem = slots;
+	}
+
+	mei_dma_copy_from(dev, buf, rd_idx, rem);
+out:
+	WRITE_ONCE(ctrl->dbuf_rd_idx, ctrl->dbuf_rd_idx + slots);
+}