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

From: Baolin Wang
Date: Fri Oct 14 2016 - 03:03:20 EST

Hi Felipe,

On 13 October 2016 at 21:34, Felipe Balbi <balbi@xxxxxxxxxx> wrote:
>
>
> Hi,
>
> Baolin Wang <baolin.wang@xxxxxxxxxx> writes:
>>> Baolin Wang <baolin.wang@xxxxxxxxxx> writes:
>>>>>> Baolin Wang <baolin.wang@xxxxxxxxxx> writes:
>>>>>>>>>> I'm thinking this is a bug in configfs interface of Gadget API, not
>>>>>>>>>> dwc3. The only reason for this to happen would be if we get to
>>>>>>>>>> ->udc_stop() with endpoints still enabled.
>>>>>>>>>>
>>>>>>>>>> Can you check if that's the case? i.e. can you check if any endpoints
>>>>>>>>>> are still enabled when we get here?
>>>>>>>>>
>>>>>>>>> No, it is not any endpoints are still enabled. Like I said in commit
>>>>>>>>> message, we will start end transfer command when disable the endpoint,
>>>>>>>>> if the end transfer command complete event comes after we have freed
>>>>>>>>> the gadget irq, it will trigger the interrupt line all the time to
>>>>>>>>> crash the system.
>>>>>>>>
>>>>>>>> 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@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxx>
> Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
> ---
> 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:

[ 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

> +
> dep->resource_index = 0;
> dep->flags &= ~DWC3_EP_BUSY;
>
> - if (dwc3_is_usb31(dwc) || dwc->revision < DWC3_REVISION_310A)
> - udelay(100);
> + if (dep->flags & DWC3_EP_KICK_POST_END_TRANSFER) {
> + dep->flags &= ~DWC3_EP_KICK_POST_END_TRANSFER;
> + ret = __dwc3_gadget_kick_transfer(dep, 0);
> + WARN_ON_ONCE(ret);
> + }
> }
>
> static void dwc3_stop_active_transfers(struct dwc3 *dwc)
> --
> 2.10.0.440.g21f862b
>
>
> --
> balbi



--
Baolin.wang
Best Regards