[PATCH v2] bus: mhi: Command completion workaround

[Loic Poulain <loic.poulain@linaro.org>]

Some buggy hardwares (e.g sdx24) may report the current command
ring wp pointer instead of the command completion pointer. It's
obviously wrong, causing completion timeout. We can however deal
with that situation by completing the cmd n-1 element, which is
what the device actually completes.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
---
 v2: Fix comment block style.

 drivers/bus/mhi/core/main.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
index 55aa7db..0f1febf 100644
--- a/drivers/bus/mhi/core/main.c
+++ b/drivers/bus/mhi/core/main.c
@@ -740,6 +740,7 @@ static void mhi_process_cmd_completion(struct mhi_controller *mhi_cntrl,
 {
 	dma_addr_t ptr = MHI_TRE_GET_EV_PTR(tre);
 	struct mhi_cmd *cmd_ring = &mhi_cntrl->mhi_cmd[PRIMARY_CMD_RING];
+	struct device *dev = &mhi_cntrl->mhi_dev->dev;
 	struct mhi_ring *mhi_ring = &cmd_ring->ring;
 	struct mhi_tre *cmd_pkt;
 	struct mhi_chan *mhi_chan;
@@ -747,6 +748,24 @@ static void mhi_process_cmd_completion(struct mhi_controller *mhi_cntrl,
 
 	cmd_pkt = mhi_to_virtual(mhi_ring, ptr);
 
+	if (unlikely(cmd_pkt == mhi_ring->wp)) {
+		/*
+		 * Some buggy hardwares (e.g sdx24) sometimes report the current
+		 * command ring wp pointer instead of the command completion
+		 * pointer. It's obviously wrong, causing completion timeout. We
+		 * can however deal with that situation by completing the cmd
+		 * n-1 element.
+		 */
+		void *ring_ptr = (void *)cmd_pkt - mhi_ring->el_size;
+
+		if (ring_ptr < mhi_ring->base)
+			ring_ptr += mhi_ring->len;
+
+		cmd_pkt = ring_ptr;
+
+		dev_warn(dev, "Bad completion pointer (ptr == ring_wp)\n");
+	}
+
 	chan = MHI_TRE_GET_CMD_CHID(cmd_pkt);
 	mhi_chan = &mhi_cntrl->mhi_chan[chan];
 	write_lock_bh(&mhi_chan->lock);
-- 
2.7.4