[PATCH 2/2] mmc: core: fall back host->f_init if failing to init mmc card after resume

[Shawn Lin <shawn.lin@rock-chips.com>]

We observed the failure of initializing card after resume
accidentally. It's hard to reproduce but we did get report from
the suspend/resume test of our RK3399 mp test farm . Unfortunately,
we still fail to figure out what was going wrong at that time.
Also we can't achieve it by retrying the host->f_init without falling
back it. But this patch will solve the problem as we could add some log
there and see that we resume the mmc card successfully after falling
back the host->f_init. There is no obvious side effect found, so it seems
this patch will improve the stability.

[   93.405085] mmc1: unexpected status 0x800900 after switch
[   93.408474] mmc1: switch to bus width 1 failed
[   93.408482] mmc1: mmc_select_hs200 failed, error -110
[   93.408492] mmc1: error -110 during resume (card was removed?)
[   93.408705] PM: resume of devices complete after 213.453 msecs

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

 drivers/mmc/core/mmc.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 403b97b..bef40c8 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1945,6 +1945,7 @@ static int mmc_suspend(struct mmc_host *host)
 static int _mmc_resume(struct mmc_host *host)
 {
 	int err = 0;
+	int i;
 
 	BUG_ON(!host);
 	BUG_ON(!host->card);
@@ -1954,8 +1955,25 @@ static int _mmc_resume(struct mmc_host *host)
 	if (!mmc_card_suspended(host->card))
 		goto out;
 
-	mmc_power_up(host, host->card->ocr);
-	err = mmc_init_card(host, host->card->ocr, host->card);
+	/*
+	 * Let's try to fallback the host->f_init
+	 * if failing to init card after resume.
+	 */
+
+	for (i = 0; i < ARRAY_SIZE(freqs); i++) {
+		if (host->f_init < freqs[i])
+			continue;
+		else
+			host->f_init = freqs[i];
+
+		mmc_power_up(host, host->card->ocr);
+		err = mmc_init_card(host, host->card->ocr, host->card);
+		if (!err)
+			break;
+
+		mmc_power_off(host);
+	}
+
 	mmc_card_clr_suspended(host->card);
 
 out:
-- 
2.3.7