mmc: mmci: Add callbacks for to manage signal voltage switch

A variant may need to define some actions before and after a voltage
switch.

This patch adds 2 callbacks to manage signal voltage switch in the struct
mmci_host_ops. ->pre_sig_volt_switch() allows to prepare a signal voltage
switch before sending the SD_SWITCH_VOLTAGE command (CMD11).
->post_sig_volt_switch callback allows specific actions to be executed,
after the I/O signal voltage level has been changed.
Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Link: https://lore.kernel.org/r/20200128090636.13689-8-ludovic.barre@st.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/mmci.c

@@ -22,6 +22,7 @@
 #include <linux/mmc/pm.h>
 #include <linux/mmc/host.h>
 #include <linux/mmc/card.h>
+#include <linux/mmc/sd.h>
 #include <linux/mmc/slot-gpio.h>
 #include <linux/amba/bus.h>
 #include <linux/clk.h>
@@ -1217,6 +1218,9 @@ mmci_start_command(struct mmci_host *host, struct mmc_command *cmd, u32 c)
 		writel_relaxed(clks, host->base + MMCIDATATIMER);
 	}
 
+	if (host->ops->pre_sig_volt_switch && cmd->opcode == SD_SWITCH_VOLTAGE)
+		host->ops->pre_sig_volt_switch(host);
+
 	if (/*interrupt*/0)
 		c |= MCI_CPSM_INTERRUPT;
 
@@ -1830,6 +1834,7 @@ static int mmci_get_cd(struct mmc_host *mmc)
 
 static int mmci_sig_volt_switch(struct mmc_host *mmc, struct mmc_ios *ios)
 {
+	struct mmci_host *host = mmc_priv(mmc);
 	int ret = 0;
 
 	if (!IS_ERR(mmc->supply.vqmmc)) {
@@ -1849,6 +1854,9 @@ static int mmci_sig_volt_switch(struct mmc_host *mmc, struct mmc_ios *ios)
 			break;
 		}
 
+		if (!ret && host->ops && host->ops->post_sig_volt_switch)
+			ret = host->ops->post_sig_volt_switch(host, ios);
+
 		if (ret)
 			dev_warn(mmc_dev(mmc), "Voltage switch failed\n");
 	}

drivers/mmc/host/mmci.h

@@ -377,6 +377,8 @@ struct mmci_host_ops {
 	void (*set_clkreg)(struct mmci_host *host, unsigned int desired);
 	void (*set_pwrreg)(struct mmci_host *host, unsigned int pwr);
 	bool (*busy_complete)(struct mmci_host *host, u32 status, u32 err_msk);
+	void (*pre_sig_volt_switch)(struct mmci_host *host);
+	int (*post_sig_volt_switch)(struct mmci_host *host, struct mmc_ios *ios);
 };
 
 struct mmci_host {