diff mbox

[RESEND,v2,2/4] mmc: core: changes frequency to hs_max_dtr when selecting hs400es

Message ID 1474589577-11193-2-git-send-email-shawn.lin@rock-chips.com (mailing list archive)
State New, archived
Headers show

Commit Message

Shawn Lin Sept. 23, 2016, 12:12 a.m. UTC
Per JESD84-B51 P69, Host need to change frequency to <=52MHz
after setting HS_TIMING to 0x1, and host may changes frequency
to <= 200MHz after setting HS_TIMING to 0x3. That means the card
expects the clock rate to increase from the current used f_init
(which is less than 400KHz, but still being less than 52MHz) to
52MHz, otherwise we find some eMMC devices significantly report
failure when sending status.

Reported-by: Xiao Yao <xiaoyao@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>

---

Changes in v2:
- improve the changelog

 drivers/mmc/core/mmc.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Doug Anderson Sept. 29, 2016, 7:47 p.m. UTC | #1
Hi,

On Thu, Sep 22, 2016 at 5:12 PM, Shawn Lin <shawn.lin@rock-chips.com> wrote:
> Per JESD84-B51 P69, Host need to change frequency to <=52MHz

Technically Page 49.  In the PDF you go to page 69, but the heading on
the top of the page says 49.

> after setting HS_TIMING to 0x1, and host may changes frequency
> to <= 200MHz after setting HS_TIMING to 0x3. That means the card
> expects the clock rate to increase from the current used f_init
> (which is less than 400KHz, but still being less than 52MHz) to
> 52MHz, otherwise we find some eMMC devices significantly report
> failure when sending status.

Technically it seems like things ought to be OK at the slow speed
since technically we're allowed to talk "high speed" at 400 kHZ (or at
any rate <= 52MHz).  ...but I guess I could also see some cards not
liking that.  Though I'm no expert, feel free to add my reviewed-by if
it is useful:

Reviewed-by: Douglas Anderson <dianders@chromium.org>
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diff mbox

Patch

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index f4ed5ac..39fc5b2 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1282,6 +1282,8 @@  static int mmc_select_hs400es(struct mmc_card *card)
 	if (err)
 		goto out_err;
 
+	mmc_set_clock(host, card->ext_csd.hs_max_dtr);
+
 	err = mmc_switch_status(card);
 	if (err)
 		goto out_err;