mmc: dw_mmc: Handle late vmmc regulators with EPROBE_DEFER

It is possible to specify a regulator that should be turned on when
dw_mmc is probed.  At the moment dw_mmc will fail to use the regulator
properly if the regulator probes after dw_mmc.  Fix this problem by
honoring EPROBE_DEFER.

At the same time move the regulator code out of the slot init code.
We only specify one regulator for the whole device and other parts of
the code (like suspend/resume) assume that the regulator has only been
enabled once.
Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

Documentation/devicetree/bindings/mmc/synopsis-dw-mshc.txt

@@ -55,6 +55,9 @@ Optional properties:
 
 * broken-cd: as documented in mmc core bindings.
 
+* vmmc-supply: The phandle to the regulator to use for vmmc.  If this is
+  specified we'll defer probe until we can find this regulator.
+
 Aliases:
 
 - All the MSHC controller nodes should be represented in the aliases node using
@@ -79,6 +82,7 @@ board specific portions as listed below.
 		broken-cd;
 		fifo-depth = <0x80>;
 		card-detect-delay = <200>;
+		vmmc-supply = <&buck8>;
 
 		slot@0 {
 			reg = <0>;

drivers/mmc/host/dw_mmc.c

@@ -1991,19 +1991,6 @@ static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)
 #endif /* CONFIG_MMC_DW_IDMAC */
 	}
 
-	host->vmmc = devm_regulator_get(mmc_dev(mmc), "vmmc");
-	if (IS_ERR(host->vmmc)) {
-		pr_info("%s: no vmmc regulator found\n", mmc_hostname(mmc));
-		host->vmmc = NULL;
-	} else {
-		ret = regulator_enable(host->vmmc);
-		if (ret) {
-			dev_err(host->dev,
-				"failed to enable regulator: %d\n", ret);
-			goto err_setup_bus;
-		}
-	}
-
 	if (dw_mci_get_cd(mmc))
 		set_bit(DW_MMC_CARD_PRESENT, &slot->flags);
 	else
@@ -2235,11 +2222,29 @@ int dw_mci_probe(struct dw_mci *host)
 		}
 	}
 
+	host->vmmc = devm_regulator_get(host->dev, "vmmc");
+	if (IS_ERR(host->vmmc)) {
+		ret = PTR_ERR(host->vmmc);
+		if (ret == -EPROBE_DEFER)
+			goto err_clk_ciu;
+
+		dev_info(host->dev, "no vmmc regulator found: %d\n", ret);
+		host->vmmc = NULL;
+	} else {
+		ret = regulator_enable(host->vmmc);
+		if (ret) {
+			if (ret != -EPROBE_DEFER)
+				dev_err(host->dev,
+					"regulator_enable fail: %d\n", ret);
+			goto err_clk_ciu;
+		}
+	}
+
 	if (!host->bus_hz) {
 		dev_err(host->dev,
 			"Platform data must supply bus speed\n");
 		ret = -ENODEV;
-		goto err_clk_ciu;
+		goto err_regulator;
 	}
 
 	host->quirks = host->pdata->quirks;
@@ -2386,6 +2391,7 @@ int dw_mci_probe(struct dw_mci *host)
 	if (host->use_dma && host->dma_ops->exit)
 		host->dma_ops->exit(host);
 
+err_regulator:
 	if (host->vmmc)
 		regulator_disable(host->vmmc);