drivers: sdhc: allow bandwidth selection

The current implementation uses both, host and card capabilites to derive
the maximum bus width to be used. However, in cases where a MMC device is
not connected to the host via shdc using the full bus width of 8 lines,
device initialization fails. Introducing the `bus-width` property
circumvents this by reducing the host bus capabilites and forcing
communication with the MMC device using 1, 4 or 8 lines.

Signed-off-by: Mourad Kharrazi <mourad.kharrazi@ithinx.io>

drivers/disk/mmc_subsys.c

@@ -21,6 +21,7 @@ enum sd_status {
 
 struct mmc_config {
 	const struct device *host_controller;
+	uint8_t bus_width;
 };
 
 struct mmc_data {
@@ -104,8 +105,10 @@ static struct disk_info mmc_disk = {
 static int disk_mmc_init(const struct device *dev)
 {
 	struct mmc_data *data = dev->data;
+	const struct mmc_config *config = dev->config;
 
 	data->status = SD_UNINIT;
+	data->card.bus_width = config->bus_width;
 	mmc_disk.dev = dev;
 	mmc_disk.name = data->name;
 
@@ -115,6 +118,7 @@ static int disk_mmc_init(const struct device *dev)
 #define DISK_ACCESS_MMC_INIT(n)						\
 	static const struct mmc_config mmc_config_##n = {			\
 		.host_controller = DEVICE_DT_GET(DT_INST_PARENT(n)),		\
+		.bus_width = DT_INST_PROP(n, bus_width),			\
 	};									\
 										\
 	static struct mmc_data mmc_data_##n = {				\

dts/bindings/sd/zephyr,mmc-disk.yaml

@@ -7,3 +7,15 @@ description: |
 compatible: "zephyr,mmc-disk"
 
 include: [sd-device.yaml]
+
+properties:
+  bus-width:
+    type: int
+    default: 8
+    description: |
+      Indicates the way the MMC device is connected to the bus.
+      Defaults to the maximum possible number of bus lines.
+    enum:
+      - 1
+      - 4
+      - 8

include/zephyr/sd/sd.h

@@ -64,6 +64,7 @@ struct sd_card {
 	enum card_status status; /*!< Card status */
 	enum card_type type; /*!< Card type */
 	uint16_t flags; /*!< Card flags */
+	uint8_t bus_width; /*!< Desired bus width */
 	uint8_t card_buffer[CONFIG_SD_BUFFER_SIZE]
 		__aligned(CONFIG_SDHC_BUFFER_ALIGNMENT); /* Card internal buffer */
 };

subsys/sd/mmc.c

@@ -380,10 +380,10 @@ static int mmc_set_bus_width(struct sd_card *card)
 	int ret;
 	struct sdhc_command cmd = {0};
 
-	if (card->host_props.host_caps.bus_8_bit_support) {
+	if (card->host_props.host_caps.bus_8_bit_support && card->bus_width == 8) {
 		cmd.arg = MMC_SWITCH_8_BIT_BUS_ARG;
 		card->bus_io.bus_width = SDHC_BUS_WIDTH8BIT;
-	} else if (card->host_props.host_caps.bus_4_bit_support) {
+	} else if (card->host_props.host_caps.bus_4_bit_support && card->bus_width >= 4) {
 		cmd.arg = MMC_SWITCH_4_BIT_BUS_ARG;
 		card->bus_io.bus_width = SDHC_BUS_WIDTH4BIT;
 	} else {