mmc: tmio: document mandatory and optional callbacks

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/tmio_mmc.h

@@ -154,8 +154,10 @@ struct tmio_mmc_host {
 	bool			native_hotplug;
 	bool			sdio_irq_enabled;
 
-	int (*write16_hook)(struct tmio_mmc_host *host, int addr);
+	/* Mandatory callback */
 	int (*clk_enable)(struct tmio_mmc_host *host);
+
+	/* Optional callbacks */
 	unsigned int (*clk_update)(struct tmio_mmc_host *host,
 				   unsigned int new_clock);
 	void (*clk_disable)(struct tmio_mmc_host *host);
@@ -164,6 +166,7 @@ struct tmio_mmc_host {
 	int (*card_busy)(struct mmc_host *mmc);
 	int (*start_signal_voltage_switch)(struct mmc_host *mmc,
 					   struct mmc_ios *ios);
+	int (*write16_hook)(struct tmio_mmc_host *host, int addr);
 };
 
 struct tmio_mmc_host *tmio_mmc_host_alloc(struct platform_device *pdev);