mmc: dw_mmc: Support setting f_min from host drivers

Host drivers may not be able to support frequencies as low as dw-mmc
supports. Unfortunately f_min isn't available when the drv_data->init
function is called, as the mmc_host struct hasn't been set up yet.

Support the host drivers saving the requested minimum frequency, so we
can later set f_min when it is available.

Signed-off-by: Peter Geis <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/dw_mmc.c

···
 	if (host->pdata->caps2)
 		mmc->caps2 = host->pdata->caps2;
 
-	mmc->f_min = DW_MCI_FREQ_MIN;
+	/* if host has set a minimum_freq, we should respect it */
+	if (host->minimum_speed)
+		mmc->f_min = host->minimum_speed;
+	else
+		mmc->f_min = DW_MCI_FREQ_MIN;
+
 	if (!mmc->f_max)
 		mmc->f_max = DW_MCI_FREQ_MAX;
 

drivers/mmc/host/dw_mmc.h

···
  * @bus_hz: The rate of @mck in Hz. This forms the basis for MMC bus
  *	rate and timeout calculations.
  * @current_speed: Configured rate of the controller.
+ * @minimum_speed: Stored minimum rate of the controller.
  * @fifoth_val: The value of FIFOTH register.
  * @verid: Denote Version ID.
  * @dev: Device associated with the MMC controller.
···
 
 	u32			bus_hz;
 	u32			current_speed;
+	u32			minimum_speed;
 	u32			fifoth_val;
 	u16			verid;
 	struct device		*dev;