On 19/08/2019 17:19, Alan Stern wrote:

On Mon, 19 Aug 2019, Roger Quadros wrote:

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On 15/08/2019 17:39, Alan Stern wrote:

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On Thu, 15 Aug 2019, Roger Quadros wrote:

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Felipe & Alan,

On 21/07/2019 21:32, Pawel Laszczak wrote:

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This patch introduce new Cadence USBSS DRD driver to linux kernel.

The Cadence USBSS DRD Controller is a highly configurable IP Core which
can be instantiated as Dual-Role Device (DRD), Peripheral Only and
Host Only (XHCI)configurations.

The current driver has been validated with FPGA burned. We have support
for PCIe bus, which is used on FPGA prototyping.

The host side of USBSS-DRD controller is compliance with XHCI
specification, so it works with standard XHCI Linux driver.

While testing this driver I encountered the following issue if I do the following.

1) USB port is "otg" and nothing connected so it is in IDLE mode to begin with.
   i.e. HCD & UDC not registered.

2) Load mass storage gadget with backing medium.
   > modprobe g_mass_storage file=lun stall=0

[   28.172142] udc-core: couldn't find an available UDC - added [g_mass_storage] to list of pending drivers

3) Connect port to PC host

...

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[   30.786313] Mass Storage Function, version: 2009/09/11
[   30.791455] LUN: removable file: (no medium)
[   31.039497] lun0: unable to open backing file: 500M.bin

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Is opening the backing file from irq_thread_fn the issue here?
If yes, how to resolve this?

I would guess that it probably is related to that.

In any case, the backing filename should be an explicit complete path.  
Who knows what the current directory will be when the actual open call
takes place?

This seems to be the case. It works fine with complete path.

Do we need to care about this in the mass storage gadget or just
rely on the user to provide the full path?

I think it's okay to rely on the user to provide the full path.

Makes sense. But kernel shouldn't segfault like so when
user unloads g_mass_storage soon after.

[   36.120594] Mass Storage Function, version: 2009/09/11
[   36.125734] LUN: removable file: (no medium)
[   36.130466] lun0: unable to open backing file: 100M.bin
[   36.135731] g_mass_storage 6000000.usb: failed to start g_mass_storage: -2
[   36.142664] cdns-usb3 6000000.usb: Failed to register USB device controller
[   36.149640] cdns-usb3 6000000.usb: set 2 has failed, back to 0root@am65xx-evm:~# modprobe -r g_mass_storage
[   60.900431] Unable to handle kernel paging request at virtual address dead000000000108
[   60.908346] Mem abort info:
[   60.911145]   ESR = 0x96000044
[   60.914227]   Exception class = DABT (current EL), IL = 32 bits
[   60.920162]   SET = 0, FnV = 0
[   60.923217]   EA = 0, S1PTW = 0
[   60.926354] Data abort info:
[   60.929228]   ISV = 0, ISS = 0x00000044
[   60.933058]   CM = 0, WnR = 1
[   60.936011] [dead000000000108] address between user and kernel address ranges
[   60.943136] Internal error: Oops: 96000044 [#1] PREEMPT SMP
[   60.948691] Modules linked in: g_mass_storage(-) usb_f_mass_storage libcomposite xhci_plat_hcd xhci_hcd usbcore ti_am335x_adc kfifo_buf omap_rng cdns3 rng_core udc_core crc32_ce xfrm_user crct10dif_ce snd_so6
[   60.993995] Process modprobe (pid: 834, stack limit = 0x00000000c2aebc69)
[   61.000765] CPU: 0 PID: 834 Comm: modprobe Not tainted 4.19.59-01963-g065f42a60499 #92
[   61.008658] Hardware name: Texas Instruments K3 J721E SoC (DT)
[   61.014472] pstate: 60000005 (nZCv daif -PAN -UAO)
[   61.019253] pc : usb_gadget_unregister_driver+0x7c/0x108 [udc_core]
[   61.025503] lr : usb_gadget_unregister_driver+0x30/0x108 [udc_core]
[   61.031750] sp : ffff00001338fda0
[   61.035049] x29: ffff00001338fda0 x28: ffff800846d40000 
[   61.040346] x27: 0000000000000000 x26: 0000000000000000 
[   61.045642] x25: 0000000056000000 x24: 0000000000000800 
[   61.050938] x23: ffff000008d7b0d0 x22: ffff0000088b07c8 
[   61.056234] x21: ffff000001100000 x20: ffff000002020260 
[   61.061530] x19: ffff0000010ffd28 x18: 0000000000000000 
[   61.066825] x17: 0000000000000000 x16: 0000000000000000 
[   61.072121] x15: 0000000000000000 x14: 0000000000000000 
[   61.077417] x13: ffff000000000000 x12: ffffffffffffffff 
[   61.082712] x11: 0000000000000030 x10: 7f7f7f7f7f7f7f7f 
[   61.088008] x9 : fefefefefefefeff x8 : 0000000000000000 
[   61.093304] x7 : ffffffffffffffff x6 : 000000000000ffff 
[   61.098599] x5 : 8080000000000000 x4 : 0000000000000000 
[   61.103895] x3 : ffff000001100020 x2 : ffff800846d40000 
[   61.109190] x1 : dead000000000100 x0 : dead000000000200 
[   61.114486] Call trace:
[   61.116922]  usb_gadget_unregister_driver+0x7c/0x108 [udc_core]
[   61.122828]  usb_composite_unregister+0x10/0x18 [libcomposite]
[   61.128643]  msg_cleanup+0x18/0xfce0 [g_mass_storage]
[   61.133682]  __arm64_sys_delete_module+0x17c/0x1f0
[   61.138458]  el0_svc_common+0x90/0x158
[   61.142192]  el0_svc_handler+0x2c/0x80
[   61.145926]  el0_svc+0x8/0xc
[   61.148794] Code: eb03003f d10be033 54ffff21 a94d0281 (f9000420) 
[   61.154869] ---[ end trace afb22e9b637bd9a7 ]---
Segmentation fault


The fix for this is below. I will post a patch for it separately.

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index af88b48c1cea..85b08756c724 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c

@@ -1137,7 +1137,7 @@ static int check_pending_gadget_drivers(struct usb_udc *udc)
 		if (!driver->udc_name || strcmp(driver->udc_name,
 						dev_name(&udc->dev)) == 0) {
 			ret = udc_bind_to_driver(udc, driver);
-			if (ret != -EPROBE_DEFER)
+			if (!ret)
 				list_del(&driver->pending);
 			break;
 		}

cheers,
-roger
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