mmc: core: more fine-grained hooks for HS400 tuning

This adds two new HS400 tuning operations:
* hs400_downgrade
* hs400_complete

These supplement the existing HS400 operation:
* prepare_hs400_tuning

This is motivated by a requirement of Renesas SDHI for the following:
1. Disabling SCC before selecting to HS if selection of HS400 has occurred.
   This can be done in an implementation of prepare_hs400_tuning_downgrade
2. Updating registers after switching to HS400
   This can be done in an implementation of complete_hs400_tuning

If hs400_downgrade or hs400_complete are not implemented then they are not
called. Thus means there should be no affect for existing drivers as none
implemt these ops.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/mmc.c

@@ -1169,6 +1169,10 @@ static int mmc_select_hs400(struct mmc_card *card)
 	/* Set host controller to HS timing */
 	mmc_set_timing(card->host, MMC_TIMING_MMC_HS);
 
+	/* Prepare host to downgrade to HS timing */
+	if (host->ops->hs400_downgrade)
+		host->ops->hs400_downgrade(host);
+
 	/* Reduce frequency to HS frequency */
 	max_dtr = card->ext_csd.hs_max_dtr;
 	mmc_set_clock(host, max_dtr);
@@ -1209,6 +1213,9 @@ static int mmc_select_hs400(struct mmc_card *card)
 	if (err)
 		goto out_err;
 
+	if (host->ops->hs400_complete)
+		host->ops->hs400_complete(host);
+
 	return 0;
 
 out_err:
@@ -1256,6 +1263,9 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
 
 	mmc_set_timing(host, MMC_TIMING_MMC_HS);
 
+	if (host->ops->hs400_downgrade)
+		host->ops->hs400_downgrade(host);
+
 	err = mmc_switch_status(card);
 	if (err)
 		goto out_err;

include/linux/mmc/host.h

@@ -146,6 +146,13 @@ 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 for switching from HS400 to HS200 */
+	void	(*hs400_downgrade)(struct mmc_host *host);
+
+	/* Complete selection of HS400 */
+	void	(*hs400_complete)(struct mmc_host *host);
+
 	/* Prepare enhanced strobe depending host driver */
 	void	(*hs400_enhanced_strobe)(struct mmc_host *host,
 					 struct mmc_ios *ios);