mmc: core: Fix eMMC initialization with 1-bit bus connection

Initializing an eMMC that's connected via a 1-bit bus is current failing,
if the HW (DT) informs that 4-bit bus is supported. In fact this is a
regression, as we were earlier capable of falling back to 1-bit mode, when
switching to 4/8-bit bus failed. Therefore, let's restore the behaviour.

Log for Samsung eMMC 5.1 chip connected via 1bit bus (only D0 pin)
Before patch:
[134509.044225] mmc0: switch to bus width 4 failed
[134509.044509] mmc0: new high speed MMC card at address 0001
[134509.054594] mmcblk0: mmc0:0001 BGUF4R 29.1 GiB
[134509.281602] mmc0: switch to bus width 4 failed
[134509.282638] I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
[134509.282657] Buffer I/O error on dev mmcblk0, logical block 0, async page read
[134509.284598] I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
[134509.284602] Buffer I/O error on dev mmcblk0, logical block 0, async page read
[134509.284609] ldm_validate_partition_table(): Disk read failed.
[134509.286495] I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
[134509.286500] Buffer I/O error on dev mmcblk0, logical block 0, async page read
[134509.288303] I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
[134509.288308] Buffer I/O error on dev mmcblk0, logical block 0, async page read
[134509.289540] I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
[134509.289544] Buffer I/O error on dev mmcblk0, logical block 0, async page read
[134509.289553]  mmcblk0: unable to read partition table
[134509.289728] mmcblk0boot0: mmc0:0001 BGUF4R 31.9 MiB
[134509.290283] mmcblk0boot1: mmc0:0001 BGUF4R 31.9 MiB
[134509.294577] I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
[134509.295835] I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
[134509.295841] Buffer I/O error on dev mmcblk0, logical block 0, async page read

After patch:

[134551.089613] mmc0: switch to bus width 4 failed
[134551.090377] mmc0: new high speed MMC card at address 0001
[134551.102271] mmcblk0: mmc0:0001 BGUF4R 29.1 GiB
[134551.113365]  mmcblk0: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 p11 p12 p13 p14 p15 p16 p17 p18 p19 p20 p21
[134551.114262] mmcblk0boot0: mmc0:0001 BGUF4R 31.9 MiB
[134551.114925] mmcblk0boot1: mmc0:0001 BGUF4R 31.9 MiB

Fixes: 577fb13 ("mmc: rework selection of bus speed mode")
Cc: [email protected]
Signed-off-by: Ivan Semenov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Ulf Hansson <[email protected]>

Author: Ivan Semenov

drivers/mmc/core/mmc.c

@@ -1015,10 +1015,12 @@ static int mmc_select_bus_width(struct mmc_card *card)
 	static unsigned ext_csd_bits[] = {
 		EXT_CSD_BUS_WIDTH_8,
 		EXT_CSD_BUS_WIDTH_4,
+		EXT_CSD_BUS_WIDTH_1,
 	};
 	static unsigned bus_widths[] = {
 		MMC_BUS_WIDTH_8,
 		MMC_BUS_WIDTH_4,
+		MMC_BUS_WIDTH_1,
 	};
 	struct mmc_host *host = card->host;
 	unsigned idx, bus_width = 0;