mmc: host: add kdoc for mmc_retune_{en|dis}able

I wanted to use it in a wrong way, so document the intended way.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20210624151616.38770-3-wsa+renesas@sang-engineering.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/host.c

@@ -96,6 +96,10 @@ void mmc_unregister_host_class(void)
 	class_unregister(&mmc_host_class);
 }
 
+/**
+ * mmc_retune_enable() - enter a transfer mode that requires retuning
+ * @host: host which should retune now
+ */
 void mmc_retune_enable(struct mmc_host *host)
 {
 	host->can_retune = 1;
@@ -127,6 +131,12 @@ void mmc_retune_unpause(struct mmc_host *host)
 }
 EXPORT_SYMBOL(mmc_retune_unpause);
 
+/**
+ * mmc_retune_disable() - exit a transfer mode that requires retuning
+ * @host: host which should not retune anymore
+ *
+ * It is not meant for temporarily preventing retuning!
+ */
 void mmc_retune_disable(struct mmc_host *host)
 {
 	mmc_retune_unpause(host);