Add write support for source/vdev/sdcard.c

[iAmInActions]

This topic was talked about before but noone actually ever finished it. I tried doing it myself but I suck at C so the only thing I actually did was causing a kernel panic whenever a write event got started. Would be nice if someone that actually knows how to work with C would add this functionality.

[Wolfvak]

I just pushed my current progress with it @ https://github.com/linux-3ds/arm9linuxfw/tree/sd-write-support, for some reason arm9linuxfw never gets the write cmd (at least not how I expect it)

last time I worked on it was maybe a week or two ago, because real life™️ got in the way, but I just wanna put this out there to let other people know I at least tried

if anyone has more info on this whole thing please make a PR to the branch? currently writes seem to be discarded (if you write to a mount and sync the filesystems, it's as if the write never happened, and if I put a debug abort in the code that writes to SD it's never triggered)

[FreddyFeuerstein]

I think I at least somewhat understand the cause:

DECLARE_VIRTDEV(
	vdev_sdcard, NULL,
	VDEV_T_BLOCK, VIRTIO_BLK_F_BLK_SIZE, 1,
	sdmc_hard_reset,
	sdmc_cfg_read, vdev_cfg_write_stub, <=== Here
	sdmc_process_vqueue
);

Its declared as a read-only device.

[Wolfvak]

nope... that's for the configuration space

much like PCI, some devices might have internal configuration bytes you can read/write to, in fact part of it is the block size (always hardcoded to 512 bytes) and the device total size in sectors

it makes sense to read from it, but at no point anything needs to be written to it (at least from what I can glance in the official spec), so the write operation is just stubbed

previously it was actually marked as a read-only device with VIRTIO_BLK_F_RO

you can see more information here https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html#x1-2390002

[FreddyFeuerstein]

That makes sence.

[FreddyFeuerstein]

Any chance that there might be write support soon?
@Wolfvak

[Wolfvak]

check the main repo, there's an experimental branch where SD card read and write work pretty well, you need the custom arm9linuxfw too

[FreddyFeuerstein]

[...] you need the custom arm9linuxfw too

The simple or the sd write support one?

[Wolfvak]

simple

[FreddyFeuerstein]

nice. thnx

[iAmInActions]

Great, I can finally run DOOM on my 3DS now! Still need to try it though.

[iAmInActions]

@Wolfvak One question: what /dev device is the SD card on now? It isn't at /dev/vda anymore.

[Wolfvak]

/dev/mmcblk0 for the SD card as a whole, /dev/mmcblk0p1 for the first partition

[iAmInActions]

@Wolfvak
no such file or directory. im using the simple branch of arm8linuxfw and the new pxi branch of the kernel.

[iAmInActions]

Is that the wrong constellation of versions or why isn't it working?

[iAmInActions]

I found out what the issue was:
I forgot to copy the .dtb files.