mmc: core: Add ->hs400_prepare_ddr() callback

Some eMMC controllers need specific settings for HS400 mode before the
speed mode can be switched to DDR mode, during the HS400 initialization
sequence. For that reason, let's introduce a new host callback,
->hs400_prepare_ddr() and invoked it just before switching to DDR mode.
Signed-off-by: Yinbo Zhu <yinbo.zhu@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/mmc.c

@@ -1181,6 +1181,9 @@ static int mmc_select_hs400(struct mmc_card *card)
 	if (err)
 		goto out_err;
 
+	if (host->ops->hs400_prepare_ddr)
+		host->ops->hs400_prepare_ddr(host);
+
 	/* Switch card to DDR */
 	err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
 			 EXT_CSD_BUS_WIDTH,

include/linux/mmc/host.h

@@ -147,6 +147,9 @@ struct mmc_host_ops {
 	/* Prepare HS400 target operating frequency depending host driver */
 	int	(*prepare_hs400_tuning)(struct mmc_host *host, struct mmc_ios *ios);
 
+	/* Prepare switch to DDR during the HS400 init sequence */
+	int	(*hs400_prepare_ddr)(struct mmc_host *host);
+
 	/* Prepare for switching from HS400 to HS200 */
 	void	(*hs400_downgrade)(struct mmc_host *host);