testing usb otg gadget (mass storage) as built in kernel module

what console log you get after inserting the module? You should select file storage gadget as module and not builtin.

             <M> USB Gadget Drivers ()  ---> 
                        File-backed Storage Gadget                               
              [M]            File-backed Storage Gadget testing version

Regards,

ajay

I had tested the usb file storage gadget as module and it is working for me.

Now. I want to build usb file storage as built-in kernel module, and test the same. To do this, I modified the default "mod_data" in "drivers/usb/gadget/file_storage.c"

mod_data = {                                  // Default values
        .transport_parm         = "BBB",
        .protocol_parm          = "SCSI",
        .removable              = 0,
        .can_stall              = 1,
        .cdrom                  = 0,
        .vendor                 = FSG_VENDOR_ID,
        .product                = FSG_PRODUCT_ID,
        .release                = 0xffff,       // Use controller chip type
        .buflen                 = 16384,
        };

To

mod_data = {                                  // Default values
        .transport_parm         = "BBB",
        .protocol_parm          = "SCSI",
        .removable              = 1,
        .can_stall              = 0,
        .cdrom                  = 0,
        .vendor                 = FSG_VENDOR_ID,
        .product                = FSG_PRODUCT_ID,
        .release                = 0xffff,       // Use controller chip type
        .buflen                 = 16384,
        };

And built and booted  the kernel, And grepped for "storage" as:

root@omap3evm:~# dmesg | grep storage
usbcore: registered new interface driver usb-storage
g_file_storage gadget: File-backed Storage Gadget, version: 20 November 2008
g_file_storage gadget: Number of LUNs=1

Now, using the sysfs,  echoed the usb_backed_file_storage path as:

root@omap3evm:~# echo /dev/mmcblk0p1 > /sys/module/g_file_storage/parameters/file

And, then, connected the usb otg cable. The usb got detected at the host side (on windows, able to see usb detect icon on taskbar and Removable Disk(E:) folder). But when try browse the Removable Disk (E:) folder it shows "Please insert a disk into drive E:".

On the debug console, as usb-otg cable is connected, following message appears.

root@omap3evm:~# g_file_storage gadget: high speed config #1

The cat for usb file storage shows

root@omap3evm:~# cat /sys/module/g_file_storage/parameters/*
N
/dev/mmcblk0p1

0
Y
N
root@omap3evm:~#

I do not see any error message, still usb file storage gadget not working, will it only work if it is build as module?

Or, missed some configuration??

Thanks                                                                                                                                                                                                                                                                                                                  Jitendra

I have no experience with the procfs or sysfs. In theory, your "file" parameter should have been picked when you plug in, ie bind().

Maybe initialize the module parameter "file" as well. This line says what to initialize:

module_param_array_named(file, mod_data.file, charp, &mod_data.num_filenames,S_IRUGO);
MODULE_PARM_DESC(file, "names of backing files or devices");

And add this to your mod_data initializers:

.file = {"/dev/mmcblk0"},
.num_filenames = 1;

I have tried the adding file  parameter initialization but it failed with error message

unable to open backing file: /dev/mmcblk0

It might have failed because the MMC has still not been detected and mounted by kernel while g_file_storage module being loaded in kernel.                                                              May loading of the  "g_file_storage" module once file system has been loaded, help.

Can the "file" parameter for g_file_storage module be specified from "bootargs" ?

Thanks                                                                                                                                                                                                                                                                                                                       Jitendra

You are probably right. The File Storage Gadget is loading before MMC. Googled about and the kernel loads builtin modules in the order that they were linked. Modifiying the link order sounds like a very grim task. Some notes here "http://www.spinics.net/lists/linux-usb/msg20860.html" but it doesn't look like a real solution.

I don't know of any bootargs that might help. I've used "rootdelay" and/or "rootwait" to wait for SD Card root device. In your case, the SD Card isn't the root device. The bootargs are documented in your Linux source in Documentation/kernel-parameters.txt.

I suppose you could modify file_storage.c to try again. I would not know how to do this properly. A work-around test is to boot-up with USB unplugged. Once boot-up, plug in the USB. The File Storage Gadget should not try to open backing store until it is plugged in, ie bind() is called.

Thanks Wong, The patch referred by you which delays the bind() operation till file system is not mounted worked. But With this approach I have to initialize the file parameter statically.

If I pass the file parameter from sysFs enrty. I see the same old Problem. The USB gadget is getting detected at Host, but when the USB gadget is browsed, it gives error "insert the disk". I modified the "mod_data" as :

 mod_data = {                                  // Default values
        .transport_parm         = "BBB",
        .protocol_parm          = "SCSI",
#ifdef CONFIG_USB_FILE_STORAGE
        .file                   ={"/dev/mmcblk0p1"},
        .removable              = 1,
        .can_stall              = 0,
#else
        .removable              = 0,
        .can_stall              = 1,
#endif
        .cdrom                  = 0,
        .vendor                 = FSG_VENDOR_ID,
        .product                = FSG_PRODUCT_ID,
        .release                = 0xffff,       // Use controller chip type
        .buflen                 = 16384,
        };

I think to support the initialization of file parameter by sysFs, The bind() operation show be delayed till the file parameter has not been initialized via sysfs. 

Thanks

Jitendra

That's good news. I think I sort of understand the functional intent now. It looks like you are building a card reader where you can control the host access to the card. Thanks for the sysfs info.