mmc: block: Add CQE support

Add CQE support to the block driver, including:
    - optionally using DCMD for flush requests
    - "manually" issuing discard requests
    - issuing read / write requests to the CQE
    - supporting block-layer timeouts
    - handling recovery
    - supporting re-tuning

CQE offers 25% - 50% better random multi-threaded I/O.  There is a slight
(e.g. 2%) drop in sequential read speed but no observable change to sequential
write.

CQE automatically sends the commands to complete requests.  However it only
supports reads / writes and so-called "direct commands" (DCMD).  Furthermore
DCMD is limited to one command at a time, but discards require 3 commands.
That makes issuing discards through CQE very awkward, but some CQE's don't
support DCMD anyway.  So for discards, the existing non-CQE approach is
taken, where the mmc core code issues the 3 commands one at a time i.e.
mmc_erase(). Where DCMD is used, is for issuing flushes.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/mmc/core/block.h b/drivers/mmc/core/block.h
index 6d34e87b18f6..f472ce5d5647 100644
--- a/drivers/mmc/core/block.h
+++ b/drivers/mmc/core/block.h
@@ -7,6 +7,8 @@ struct request;
 
 void mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req);
 
+void mmc_blk_cqe_recovery(struct mmc_queue *mq);
+
 enum mmc_issued;
 
 enum mmc_issued mmc_blk_mq_issue_rq(struct mmc_queue *mq, struct request *req);