VFS: Cannot open root device "mmcblk0p2" or unknown-block(179,2): error -2

What I am trying to do is to have a working Linux kernel with rootfs running on STM32F769I discovery board.

I built the u-boot, kernel and device tree for it using Buildroot, it has been an uphill struggle for me because I am a beginner with embedded systems.

I have managed to get it to the point where the kernel has to mount the rootfs partition from SD card, but it is unable to do so the boot partition here is set correctly and it is even recognized by the kernel but somehow the kernel still panics and is unable to read it.

On the SD card there are two partitions:

mmcblk0p1: vfat
mmcblk0p2: ext3

Kernel boot log:

Starting kernel ...

Booting Linux on physical CPU 0x0
Linux version 5.4.61 (zjerina@debian) (gcc version 8.4.0 (Buildroot 2020.02.5)) #1 PREEMPT Thu Sep 10 17:22:19 EDT 2020
CPU: ARMv7-M [411fc270] revision 0 (ARMv7M), cr=00000000
CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache
OF: fdt: Machine model: STMicroelectronics STM32F769-DISCO board
On node 0 totalpages: 4096
  Normal zone: 32 pages used for memmap
  Normal zone: 0 pages reserved
  Normal zone: 4096 pages, LIFO batch:0
pcpu-alloc: s0 r0 d32768 u32768 alloc=1*32768
pcpu-alloc: [0] 0 
Built 1 zonelists, mobility grouping off.  Total pages: 4064
Kernel command line: console=ttySTM0,115200n8 noinitrd root=/dev/mmcblk0p2 rootfstype=ext3 rw rootwait rootdelay=60 loglevel=60
Dentry cache hash table entries: 2048 (order: 1, 8192 bytes, linear)
Inode-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
mem auto-init: stack:off, heap alloc:off, heap free:off
Memory: 12784K/16384K available (2278K kernel code, 170K rwdata, 544K rodata, 104K init, 117K bss, 3600K reserved, 0K cma-reserved)
SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
rcu: Preemptible hierarchical RCU implementation.
        Tasks RCU enabled.
rcu: RCU calculated value of scheduler-enlistment delay is 10 jiffies.
NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
/soc/interrupt-controller@40013c00: bank0
random: get_random_bytes called from 0xc02ee535 with crng_init=0
clocksource: arm_system_timer: mask: 0xffffff max_cycles: 0xffffff, max_idle_ns: 298634427 ns
ARM System timer initialized as clocksource
sched_clock: 32 bits at 100MHz, resolution 10ns, wraps every 21474836475ns
timer@40000c00: STM32 sched_clock registered
Switching to timer-based delay loop, resolution 10ns
timer@40000c00: STM32 delay timer registered
clocksource: timer@40000c00: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604467 ns
/soc/timer@40000c00: STM32 clockevent driver initialized (32 bits)
Calibrating delay loop (skipped), value calculated using timer frequency.. 200.00 BogoMIPS (lpj=1000000)
pid_max: default: 4096 minimum: 301
Mount-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
rcu: Hierarchical SRCU implementation.
devtmpfs: initialized
clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
pinctrl core: initialized pinctrl subsystem
NET: Registered protocol family 16
stm32f769-pinctrl soc:pin-controller: No package detected, use default one
stm32f769-pinctrl soc:pin-controller: GPIOA bank added
stm32f769-pinctrl soc:pin-controller: GPIOB bank added
stm32f769-pinctrl soc:pin-controller: GPIOC bank added
stm32f769-pinctrl soc:pin-controller: GPIOD bank added
stm32f769-pinctrl soc:pin-controller: GPIOE bank added
stm32f769-pinctrl soc:pin-controller: GPIOF bank added
stm32f769-pinctrl soc:pin-controller: GPIOG bank added
stm32f769-pinctrl soc:pin-controller: GPIOH bank added
stm32f769-pinctrl soc:pin-controller: GPIOI bank added
stm32f769-pinctrl soc:pin-controller: GPIOJ bank added
stm32f769-pinctrl soc:pin-controller: GPIOK bank added
stm32f769-pinctrl soc:pin-controller: Pinctrl STM32 initialized
clocksource: Switched to clocksource timer@40000c00
NET: Registered protocol family 2
tcp_listen_portaddr_hash hash table entries: 512 (order: 0, 4096 bytes, linear)
TCP established hash table entries: 1024 (order: 0, 4096 bytes, linear)
TCP bind hash table entries: 1024 (order: 0, 4096 bytes, linear)
TCP: Hash tables configured (established 1024 bind 1024)
UDP hash table entries: 256 (order: 0, 4096 bytes, linear)
UDP-Lite hash table entries: 256 (order: 0, 4096 bytes, linear)
NET: Registered protocol family 1
workingset: timestamp_bits=30 max_order=12 bucket_order=0
fuse: init (API version 7.31)
io scheduler mq-deadline registered
io scheduler kyber registered
STM32 USART driver initialized
40011000.serial: ttySTM0 at MMIO 0x40011000 (irq = 35, base_baud = 6250000) is a stm32-usart
printk: console [ttySTM0] enabled
stm32-usart 40011000.serial: rx dma alloc failed
stm32-usart 40011000.serial: interrupt mode used for rx (no dma)
stm32-usart 40011000.serial: tx dma alloc failed
stm32-usart 40011000.serial: interrupt mode used for tx (no dma)
libphy: Fixed MDIO Bus: probed
stm32_rtc 40002800.rtc: registered as rtc0
stm32_rtc 40002800.rtc: Date/Time must be initialized
i2c /dev entries driver
stm32f7-i2c 40005400.i2c: can't use DMA
stm32f7-i2c 40005400.i2c: STM32F7 I2C-0 bus adapter
mmci-pl18x 40011c00.sdio2: Got CD GPIO
mmci-pl18x 40011c00.sdio2: mmc0: PL180 manf 80 rev8 at 0x40011c00 irq 36,0 (pio)
mmci-pl18x 40011c00.sdio2: DMA channels RX none, TX none
mmc0: host does not support reading read-only switch, assuming write-enable
mmc0: new SDHC card at address aaaa
input: gpio_keys as /devices/platform/gpio_keys/input/input0
mmcblk0: mmc0:aaaa SL08G 7.40 GiB 
stm32_rtc 40002800.rtc: setting system clock to 2000-01-01T00:38:58 UTC (946687138)
 mmcblk0: p1 p2
Warning: unable to open an initial console.
Waiting 60 sec before mounting root device...
random: fast init done
Failed to create /dev/root: -2
VFS: Cannot open root device "mmcblk0p2" or unknown-block(179,2): error -2
Please append a correct "root=" boot option; here are the available partitions:
b300         7761920 mmcblk0 
 driver: mmcblk
  b301           51200 mmcblk0p1 d7154cc1-01

  b302         7709696 mmcblk0p2 d7154cc1-02

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(179,2)
---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(179,2) ]---