Hi Shawn,
On 12/20/2016 12:59 PM, Shawn Lin wrote:
On 2016/12/20 13:53, Ritesh Harjani wrote:
Currently mmc_select_hs400es is not setting the desired frequency
before sending switch command. This makes CMD13 to timeout on
some controllers.
Thus add a change to set the desired HS400 frequency
in mmc_select_hs400es when the timing is switched to HS400.
What is the desired HS400 freq? I guess it is 200MHz, right?
Well, per the spec, it just say "host *may* changes frequency to
<= 200Mhz". So before setting timing to MMC_TIMING_MMC_HS400, we
already reach ext_csd.hs_max_dtr. So it should meet the spec. If
the fact that some controllers would see CMD13 timeout here, I guess
you wouldn't let folks add max-frequency to the DT as if the max freq
is set to just lower than your *desired HS400 freq* , it the same
failure result even you add this patch, right?
the root cause the controllers see failure for CMD13 is it didn't
configure the right delay phase or something similar to fit the timing
under the freq of hs_max_dtr, I guess.
Actually this may be limitation of sdhc msm controller that it cannot
work at lower frequency while in HS400 mode. I would have to see more on
this to confirm on why this limitation is there (mostly it was with some
DLL limitation).
In that case maybe I should not generalize this for other controllers.
But still the below code change to set the bus_speed after setting the
timing should be fine right ? Since host controller may as well change
the frequency to 200MHz.
Do you think the below change is fine in this sense? I can change the
commit message to just -
"set both timing mode and frequency before sending CMD13 in
mmc_select_hs400es."
Or do you see any other approach to this ?
Regards
Ritesh
Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxxx>
---
drivers/mmc/core/mmc.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index b61b52f9..eb69497 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1329,6 +1329,7 @@ static int mmc_select_hs400es(struct mmc_card
*card)
/* Set host controller to HS400 timing and frequency */
mmc_set_timing(host, MMC_TIMING_MMC_HS400);
+ mmc_set_bus_speed(card);
/* Controller enable enhanced strobe function */
host->ios.enhanced_strobe = true;
--
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