linux-kernel - [PATCH 3/5] mmc: core: changes frequency to hs_max

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Date:   Wed, 21 Sep 2016 09:43:51 +0800
From:   Shawn Lin <shawn.lin@...k-chips.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Shawn Lin <shawn.lin@...k-chips.com>
Subject: [PATCH 3/5] 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. It seems there is no difference if
we don't change frequency to <= 52MHz as f_init is already less than
52MHz. But actually it does make difference. When doing compatibility
test we see failures for some eMMC devices without changing the
frequency to hs_max_dtr. And let's read the spec again, we could see
that "Host may changes frequency to 200MHz" implies that it's not
mandatory. But the "Host need to change frequency to <= 52MHz" implies
that we should do this.

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

 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 3163bb9..989d37e 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