mmc: sdhci: allow for eMMC 74 clock generation by controller

Snippet of code for how adaptation layer should handle the call:
/*
 * eMMC spec calls for the host to send 74 clocks to the card
 * during initialization, right after voltage stabilization.
 * create the clocks manually right here.
 */
void generate_init_clocks_A0(struct sdhci_host *host, u8 power_mode)
{
	struct sdhci_mmc_slot *slot = sdhci_priv(host);

	if (slot->power_mode == MMC_POWER_UP &&
	    power_mode == MMC_POWER_ON) {
		/* controller specific code here */
		/* slot->power_mode holds previous power setting */
	}
	slot->power_mode = power_mode;
}

Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/sdhci.c

@@ -1182,6 +1182,9 @@ static void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 	else
 		sdhci_set_power(host, ios->vdd);
 
+	if (host->ops->platform_send_init_74_clocks)
+		host->ops->platform_send_init_74_clocks(host, ios->power_mode);
+
 	ctrl = sdhci_readb(host, SDHCI_HOST_CONTROL);
 
 	if (ios->bus_width == MMC_BUS_WIDTH_8)

drivers/mmc/host/sdhci.h

@@ -212,6 +212,8 @@ struct sdhci_ops {
 	unsigned int	(*get_max_clock)(struct sdhci_host *host);
 	unsigned int	(*get_min_clock)(struct sdhci_host *host);
 	unsigned int	(*get_timeout_clock)(struct sdhci_host *host);
+	void (*platform_send_init_74_clocks)(struct sdhci_host *host,
+					     u8 power_mode);
 };
 
 #ifdef CONFIG_MMC_SDHCI_IO_ACCESSORS