linux-kernel - [PATCH v2 2/4] mmc: core: changes frequency to hs_max

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Date:   Fri, 23 Sep 2016 08:03:09 +0800
From:   Shawn Lin <shawn.lin@...k-chips.com>
To:     Jaehoon Chung <jh80.chung@...sung.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Shawn Lin <shawn.lin@...k-chips.com>
Subject: [PATCH v2 2/4] mmc: core: changes frequency to hs_max_dtr when selecting hs400es

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@...k-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>

---

Changes in v2:
- improve the changelog

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

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;
-- 
2.3.7