mmc: msm_sdcc: add support for AUTO_CMD21
Using HS200 (supported by eMMC 4.5 spec compliant cards) bus speed
mode requires DLL (Delay Locked Loop for sampling clock generation) HW
block to be tuned if clock rate is >100MHz so that both host and card
are in sync. eMMC 4.5 spec has added CMD21 for this tuning mechanism.
During card initialization, driver uses the tuning command to search
for an optimal sampling point and then programs the DLL HW with this
optimal sampling point.
In addition, msm SDCC controller's DLL HW has a mechansim for data
tracking (CDR) which can be enabled during read transactions so the host
will not lose the sampling point as a result of voltage and, especially,
temperature variations. Tuning pattern command (CMD21) can be sent
automatically by HW (by using AUTO_CMD21 bit) before any RX transaction
to help CDR keep track of the correct sampling point.
Since sending CMD21 automatically before every read commands is an
overhead, reducing read performance by ~1 MB/s and eMMC spec does not
mandate sending the tuning command before every read operation, this
change adds support for AUTO_CMD21 (and keeps it disabled by default)
while providing a sysfs attribute to enable or disable AUTO_CMD21 as
needed.
Change-Id: I6e053db8878b273a407fa7caf8332eb064f351ce
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>
2 files changed