sdhci: Add support for hosts that are only capable of 1-bit transfers

Some hosts (hardware configurations, or particular SD/MMC slots) may
not support 4-bit bus. For example, on MPC8569E-MDS boards we can
switch between serial (1-bit only) and nibble (4-bit) modes, thought
we have to disable more peripherals to work in 4-bit mode.

Along with some small core changes, this patch modifies sdhci-of
driver, so that now it looks for "sdhci,1-bit-only" property in the
device-tree, and if specified we enable a proper quirk.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>

Documentation/powerpc/dts-bindings/fsl/esdhc.txt

@@ -10,6 +10,8 @@ Required properties:
   - interrupts : should contain eSDHC interrupt.
   - interrupt-parent : interrupt source phandle.
   - clock-frequency : specifies eSDHC base clock frequency.
+  - sdhci,1-bit-only : (optional) specifies that a controller can
+    only handle 1-bit data transfers.
 
 Example:
 

drivers/mmc/host/sdhci-of.c

@@ -250,6 +250,9 @@ static int __devinit sdhci_of_probe(struct of_device *ofdev,
 		host->ops = &sdhci_of_data->ops;
 	}
 
+	if (of_get_property(np, "sdhci,1-bit-only", NULL))
+		host->quirks |= SDHCI_QUIRK_FORCE_1_BIT_DATA;
+
 	clk = of_get_property(np, "clock-frequency", &size);
 	if (clk && size == sizeof(*clk) && *clk)
 		of_host->clock = *clk;

drivers/mmc/host/sdhci.c

@@ -1761,7 +1761,10 @@ int sdhci_add_host(struct sdhci_host *host)
 	mmc->ops = &sdhci_ops;
 	mmc->f_min = host->max_clk / 256;
 	mmc->f_max = host->max_clk;
-	mmc->caps = MMC_CAP_4_BIT_DATA | MMC_CAP_SDIO_IRQ;
+	mmc->caps = MMC_CAP_SDIO_IRQ;
+
+	if (!(host->quirks & SDHCI_QUIRK_FORCE_1_BIT_DATA))
+		mmc->caps |= MMC_CAP_4_BIT_DATA;
 
 	if (caps & SDHCI_CAN_DO_HISPD)
 		mmc->caps |= MMC_CAP_SD_HIGHSPEED;

drivers/mmc/host/sdhci.h

@@ -228,6 +228,8 @@ struct sdhci_host {
 #define SDHCI_QUIRK_FORCE_BLK_SZ_2048			(1<<20)
 /* Controller cannot do multi-block transfers */
 #define SDHCI_QUIRK_NO_MULTIBLOCK			(1<<21)
+/* Controller can only handle 1-bit data transfers */
+#define SDHCI_QUIRK_FORCE_1_BIT_DATA			(1<<22)
 
 	int			irq;		/* Device IRQ */
 	void __iomem *		ioaddr;		/* Mapped address */