Re: [PATCH v2] usb: dwc3: gadget: Wait for end transfer complete before free irq

[Felipe Balbi <balbi@kernel.org>]

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Hi,

Baolin Wang <baolin.wang@linaro.org> writes:
>>>>>>>>> I see what the problem is. Databook tells us we *must* set CMDIOC when
>>>>>>>>> issuing EndTransfer command and we should always wait for Command
>>>>>>>>> Complete IRQ. However, we took a shortcut and just delayed for 100us
>>>>>>>>> after issuing End Transfer.
>>>>>>>>
>>>>>>>> Yes, but 100us delay is not enough in some scenarios, like changing
>>>>>>>> function with configfs frequently, we will met problems.
>>>>>>>
>>>>>>> heh, 100us *is* enough. However we still get an IRQ because we requested
>>>>>>> for it. If you want to fix this, then you need to find a way to get rid
>>>>>>> of that 100us udelay() and add a proper wait_for_completion() to delay
>>>>>>> execution until command complete IRQ fires up.
>>>>>>
>>>>>> I haven't tested this yet, but it shows the idea (I think we might still
>>>>>> have a race with ep_queue if we're still waiting for End Transfer, but
>>>>>
>>>>> Yes, maybe we need check DWC3_EP_END_TRANSFER_PENDING flag when
>>>>> queuing one request.
>>>>
>>>> Yeah, I'll add that check later. I still need to make sure we would
>>>> still try to kick any transfers that might have been queued while
>>>> waiting for End Transfer Command Complete IRQ.
>>>
>>> OK. But I still worried if there are other races in some places which
>>
>> There are no other places where this needs to be sorted out.
>>
>>> is not easy to find out by testing. No introducing race condition
>>> would be one better solution, anyway I would like to test the patch
>>> you send out firstly.
>>
>> Right, but your patch was working around another problem, rather then
>> fixing it.
>>
>> Here's another version which should make sure everything remains working
>> as it should.
>>
>> 8<------------------------------------------------------------------------
>> From 1f922a902a21d5cee32082be18bbfbf1d46137e4 Mon Sep 17 00:00:00 2001
>> From: Felipe Balbi <felipe.balbi@linux.intel.com>
>> Date: Thu, 13 Oct 2016 14:09:47 +0300
>> Subject: [PATCH] usb: dwc3: gadget: wait for End Transfer to complete
>>
>> Instead of just delaying for 100us, we should
>> actually wait for End Transfer Command Complete
>> interrupt before moving on. Note that this should
>> only be done if we're dealing with one of the core
>> revisions that actually require the interrupt before
>> moving on.
>>
>> Reported-by: Baolin Wang <baolin.wang@linaro.org>
>> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
>> ---
>>  drivers/usb/dwc3/core.h   | 10 +++++++++-
>>  drivers/usb/dwc3/gadget.c | 31 ++++++++++++++++++++++++++++---
>>  2 files changed, 37 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
>> index e878366ead00..cf495d932252 100644
>> --- a/drivers/usb/dwc3/core.h
>> +++ b/drivers/usb/dwc3/core.h
>> @@ -26,6 +26,7 @@
>>  #include <linux/dma-mapping.h>
>>  #include <linux/mm.h>
>>  #include <linux/debugfs.h>
>> +#include <linux/wait.h>
>>
>>  #include <linux/usb/ch9.h>
>>  #include <linux/usb/gadget.h>
>> @@ -504,6 +505,7 @@ struct dwc3_event_buffer {
>>   * @endpoint: usb endpoint
>>   * @pending_list: list of pending requests for this endpoint
>>   * @started_list: list of started requests on this endpoint
>> + * @wait_end_transfer: wait_queue_head_t for waiting on End Transfer complete
>>   * @lock: spinlock for endpoint request queue traversal
>>   * @regs: pointer to first endpoint register
>>   * @trb_pool: array of transaction buffers
>> @@ -529,6 +531,8 @@ struct dwc3_ep {
>>         struct list_head        pending_list;
>>         struct list_head        started_list;
>>
>> +       wait_queue_head_t       wait_end_transfer;
>> +
>>         spinlock_t              lock;
>>         void __iomem            *regs;
>>
>> @@ -545,7 +549,8 @@ struct dwc3_ep {
>>  #define DWC3_EP_BUSY           (1 << 4)
>>  #define DWC3_EP_PENDING_REQUEST        (1 << 5)
>>  #define DWC3_EP_MISSED_ISOC    (1 << 6)
>> -
>> +#define DWC3_EP_END_TRANSFER_PENDING (1 << 7)
>> +#define DWC3_EP_KICK_POST_END_TRANSFER (1 << 8)
>>         /* This last one is specific to EP0 */
>>  #define DWC3_EP0_DIR_IN                (1 << 31)
>>
>> @@ -1047,6 +1052,9 @@ struct dwc3_event_depevt {
>>  #define DEPEVT_TRANSFER_BUS_EXPIRY     2
>>
>>         u32     parameters:16;
>> +
>> +/* For Command Complete Events */
>> +#define DEPEVT_PARAMETER_CMD(n) (((n) & (0xf << 24)) >> 24)
>>  } __packed;
>>
>>  /**
>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>> index 3ba05b12e49a..a3f81b5ba901 100644
>> --- a/drivers/usb/dwc3/gadget.c
>> +++ b/drivers/usb/dwc3/gadget.c
>> @@ -598,6 +598,8 @@ static int __dwc3_gadget_ep_enable(struct dwc3_ep *dep,
>>                 reg |= DWC3_DALEPENA_EP(dep->number);
>>                 dwc3_writel(dwc->regs, DWC3_DALEPENA, reg);
>>
>> +               init_waitqueue_head(&dep->wait_end_transfer);
>> +
>>                 if (usb_endpoint_xfer_control(desc))
>>                         return 0;
>>
>> @@ -1151,6 +1153,11 @@ static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct dwc3_request *req)
>>         if (!dwc3_calc_trbs_left(dep))
>>                 return 0;
>>
>> +       if (dep->flags & DWC3_EP_END_TRANSFER_PENDING) {
>> +               dep->flags &= DWC3_EP_KICK_POST_END_TRANSFER;
>> +               return 0;
>> +       }
>> +
>>         ret = __dwc3_gadget_kick_transfer(dep, 0);
>>         if (ret && ret != -EBUSY)
>>                 dwc3_trace(trace_dwc3_gadget,
>> @@ -2156,6 +2163,7 @@ static void dwc3_endpoint_interrupt(struct dwc3 *dwc,
>>  {
>>         struct dwc3_ep          *dep;
>>         u8                      epnum = event->endpoint_number;
>> +       u8                      cmd;
>>
>>         dep = dwc->eps[epnum];
>>
>> @@ -2200,8 +2208,13 @@ static void dwc3_endpoint_interrupt(struct dwc3 *dwc,
>>                         return;
>>                 }
>>                 break;
>> -       case DWC3_DEPEVT_RXTXFIFOEVT:
>>         case DWC3_DEPEVT_EPCMDCMPLT:
>> +               cmd = DEPEVT_PARAMETER_CMD(event->parameters);
>> +
>> +               if (cmd == DWC3_DEPCMD_ENDTRANSFER)
>> +                       dep->flags &= ~DWC3_EP_END_TRANSFER_PENDING;
>
> I think you missed wake_up(&dep->wait_end_transfer) function here.
>
>> +               break;
>> +       case DWC3_DEPEVT_RXTXFIFOEVT:
>>                 break;
>>         }
>>  }
>> @@ -2246,6 +2259,7 @@ static void dwc3_reset_gadget(struct dwc3 *dwc)
>>  }
>>
>>  static void dwc3_stop_active_transfer(struct dwc3 *dwc, u32 epnum, bool force)
>> +__releases(&dwc->lock) __acquires(&dwc->lock)
>>  {
>>         struct dwc3_ep *dep;
>>         struct dwc3_gadget_ep_cmd_params params;
>> @@ -2295,11 +2309,22 @@ static void dwc3_stop_active_transfer(struct dwc3 *dwc, u32 epnum, bool force)
>>         memset(&params, 0, sizeof(params));
>>         ret = dwc3_send_gadget_ep_cmd(dep, cmd, &params);
>>         WARN_ON_ONCE(ret);
>> +
>> +       if (dwc3_is_usb31(dwc) || dwc->revision < DWC3_REVISION_310A) {
>> +               dep->flags |= DWC3_EP_END_TRANSFER_PENDING;
>> +               wait_event_lock_irq(dep->wait_end_transfer,
>> +                               !(dep->flags & DWC3_EP_END_TRANSFER_PENDING),
>> +                               dwc->lock);
>> +       }
>
> I've tested your patch, unfortunately it can not work on my platform.
> Since we can not issue wait_event_lock_irq() function in atomic
> context, we will hold another 'cdev->lock' in composite_disconnect()
> function. The dump stack as below:

argh, we have nested spinlocks :-( Well, we shouldn't call
usb_ep_disable() with locks held AFAICR. So the following should be
enough:

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 919d7d1b611c..2e9359c58eb9 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -732,8 +732,10 @@ static void reset_config(struct usb_composite_dev *cdev)
        DBG(cdev, "reset config\n");
 
        list_for_each_entry(f, &cdev->config->functions, list) {
+               spin_unlock_irq(&cdev->lock);
                if (f->disable)
                        f->disable(f);
+               spin_lock_irq(&cdev->lock);
 
                bitmap_zero(f->endpoints, 32);
        }

Alan, do you remember if we have a requirement for not holding locks
when calling usb_ep_disable()? I can't find Documentation about it, but
history shows me that usb_ep_disable() was called without locks and IRQs
enabled. Do you think we should update documentation about this?

(keeping dump below)

> [   92.686810] c7 BUG: scheduling while atomic: init/1/0x00000002
> [   92.686825] c7 INFO: lockdep is turned off.
> [   92.686833] c0 Modules linked in: mtty marlin2_fm mali_kbase(O)
> [   92.686859] c0 Preemption disabled at:[<ffffffc00064cea8>] composite_disconnect+0x30/0x90
> [   92.686879] c7
> [   92.686891] c7 CPU: 7 PID: 1 Comm: init Tainted: G        W  O    4.4.6+ #20
> [   92.686898] c7 Hardware name: Spreadtrum SP9860g Board (DT)
> [   92.686905] c7 Call trace:
> [   92.689519] c7 [<ffffffc00008b538>] dump_backtrace+0x0/0x170
> [   92.689528] c7 [<ffffffc00008b6c8>] show_stack+0x20/0x28
> [   92.689537] c7 [<ffffffc000424114>] dump_stack+0xa8/0xe0
> [   92.689547] c7 [<ffffffc0000fa7d8>] __schedule_bug+0x7c/0xd4
> [   92.689559] c7 [<ffffffc000aa5d20>] __schedule+0x724/0xab4
> [   92.689567] c7 [<ffffffc000aa62f8>] schedule+0x48/0xa8
> [   92.689578] c7 [<ffffffc000625fb8>] dwc3_stop_active_transfer.constprop.27+0x98/0x158
> [   92.689587] c7 [<ffffffc000626c88>] dwc3_remove_requests+0x3c/0xa0
> [   92.689595] c7 [<ffffffc000627d08>] __dwc3_gadget_ep_disable+0x4c/0x12c
> [   92.689603] c7 [<ffffffc000628188>] dwc3_gadget_ep_disable+0x6c/0x100
> [   92.689613] c7 [<ffffffc0006708b4>] mtp_function_disable+0xc0/0x100
> [   92.689624] c7 [<ffffffc00064bfa0>] reset_config+0x4c/0x94
> [   92.689632] c7 [<ffffffc00064cebc>] composite_disconnect+0x44/0x90
> [   92.689641] c7 [<ffffffc0006509c4>] android_disconnect+0x60/0x70
> [   92.689649] c7 [<ffffffc000653080>] usb_gadget_remove_driver+0x6c/0xe0
> [   92.689657] c7 [<ffffffc000653170>] usb_gadget_unregister_driver+0x7c/0xc8
> [   92.689665] c7 [<ffffffc000651adc>] gadget_dev_desc_UDC_store+0x8c/0x128
> [   92.689675] c7 [<ffffffc0002c263c>] configfs_write_file+0xd0/0x13c
> [   92.689684] c7 [<ffffffc00023cb14>] vfs_write+0xb8/0x214
> [   92.689692] c7 [<ffffffc00023d594>] SyS_write+0x54/0xb0
> [   92.689701] c7 [<ffffffc000085ff0>] el0_svc_naked+0x24/0x28

-- 
balbi

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