mmc: Limit MMC speed to 52MHz if not HS200

If "caps2" host capabilities does not indicate support for MMC
HS200, don't allow clock speeds >52MHz. Currently, for MMC, the
clock speed is set to the lesser of the max speed the eMMC module
supports (card->ext_csd.hs_max_dtr) or the max base clock of the
host controller (host->f_max based on BASE_CLK_FREQ in the host
CAPS register). This means that a host controller that doesn't
support HS200 mode but has a base clock of 100MHz and an eMMC module
that supports HS200 speeds will end up using a 100MHz clock.
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/mmc.c

@@ -1066,6 +1066,8 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 	if (mmc_card_highspeed(card) || mmc_card_hs200(card)) {
 		if (max_dtr > card->ext_csd.hs_max_dtr)
 			max_dtr = card->ext_csd.hs_max_dtr;
+		if (mmc_card_highspeed(card) && (max_dtr > 52000000))
+			max_dtr = 52000000;
 	} else if (max_dtr > card->csd.max_dtr) {
 		max_dtr = card->csd.max_dtr;
 	}