linux-kernel - Re: [PATCH v3 1/1] usb: xhci: Add Clear_TT

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Message-ID: <e82d0e4b-3621-ed5b-b25c-ebf3feec91bd@nvidia.com>
Date:   Thu, 2 May 2019 20:32:56 +0800
From:   Jim Lin <jilin@...dia.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v3 1/1] usb: xhci: Add Clear_TT_Buffer



On 2019年05月02日 18:56, Mathias Nyman wrote:
> On 30.4.2019 6.06, Jim Lin wrote:
>> USB 2.0 specification chapter 11.17.5 says "as part of endpoint halt
>> processing for full-/low-speed endpoints connected via a TT, the host
>> software must use the Clear_TT_Buffer request to the TT to ensure
>> that the buffer is not in the busy state".
>
> Good point, xhci isn't making sure TT buffers get cleared when they 
> should.
>
>>
>> In our case, a full-speed speaker (ConferenceCam) is behind a high-
>> speed hub (ConferenceCam Connect), sometimes once we get STALL on a
>> request we may continue to get STALL with the folllowing requests,
>> like Set_Interface.
>>
>> Here we add Clear_TT_Buffer for the following Set_Interface requests
>> to get ACK successfully.
>>
>> Signed-off-by: Jim Lin <jilin@...dia.com>
>> ---
>> v2: xhci_clear_tt_buffer_complete: add static, shorter indentation
>>      , remove its claiming in xhci.h
>> v3: Add description for clearing_tt (xhci.h)
>>
>>   drivers/usb/host/xhci-ring.c | 28 ++++++++++++++++++++++++++++
>>   drivers/usb/host/xhci.c      |  7 +++++++
>>   drivers/usb/host/xhci.h      |  2 ++
>>   3 files changed, 37 insertions(+)
>>
>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
>> index 9215a28dad40..02b1ebad81e7 100644
>> --- a/drivers/usb/host/xhci-ring.c
>> +++ b/drivers/usb/host/xhci-ring.c
>> @@ -1786,6 +1786,33 @@ struct xhci_segment *trb_in_td(struct xhci_hcd 
>> *xhci,
>>       return NULL;
>>   }
>>   +static void xhci_clear_hub_tt_buffer(struct xhci_hcd *xhci,
>> +    unsigned int slot_id, struct xhci_td *td)
>> +{
>> +    struct xhci_virt_device *dev;
>> +    struct xhci_slot_ctx *slot_ctx;
>> +    int saved_devnum;
>> +
>> +    /*
>> +     * As part of low/full-speed endpoint-halt processing
>> +     * we must clear the TT buffer (USB 2.0 specification 11.17.5).
>> +     */
>> +    if (td->urb->dev->tt && !usb_pipeint(td->urb->pipe) &&
>> +        (td->urb->dev->tt->hub != xhci_to_hcd(xhci)->self.root_hub) &&
>> +        !xhci->clearing_tt) {
>> +        xhci->clearing_tt = 1;
>
> one xhci->clearing_tt under is not enough, there might be several HS 
> hubs, or
> multi TT hubs with halted endpoints at the same time that need TT 
> clearing.
>
> How about a flag per endpoint?
>
> For example Aadding a EP_CLEARING_TT flag for ep_state in struct 
> xhci_virt_ep?
> just like EP_STOP_CMD_PENDING, or EP_HALTED
>
>> +        dev = xhci->devs[slot_id];
>> +        slot_ctx = xhci_get_slot_ctx(xhci, dev->out_ctx);
>> +        /* Update devnum temporarily for usb_hub_clear_tt_buffer */
>> +        saved_devnum = td->urb->dev->devnum;
>> +        td->urb->dev->devnum = (int) le32_to_cpu(slot_ctx->dev_state) &
>> +            DEV_ADDR_MASK;
>
> Changing the struct usb_device devnum on the fly seems like a bit of a 
> hack, and probably
> causes issues elsewhere. Devnum is tied to uevents, usbfs, sysfs etc.
>
> We need another solution, some options:
>
> - Let usb_hub_clear_tt_buffer() figure out address and not just use 
> devnum if host == xhci.
> - Add address to struct usb_device, (would have both address and 
> devnum), use it when needed.
> - Provide address as parameter to usb_clear_tt_buffer() (api change, 
> changes other host drivers)
> - Force devnum to be same as address, usb core can't choose address 
> for xhci devices.
>
> -Mathias
Thanks for review. Will try.

--nvpublic