linux-kernel - Re: [PATCH v9 2/2] usb: xhci: Add Clear_TT

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Date:   Fri, 10 May 2019 10:23:19 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Jim Lin <jilin@...dia.com>
cc:     gregkh@...uxfoundation.org, <mathias.nyman@...el.com>,
        <kai.heng.feng@...onical.com>, <drinkcat@...omium.org>,
        <keescook@...omium.org>, <nsaenzjulienne@...e.de>,
        <jflat@...omium.org>, <malat@...ian.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 2/2] usb: xhci: Add Clear_TT_Buffer

On Fri, 10 May 2019, 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".
> 
> 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 update udev->devaddr in address_device callback function
> (this USB device address is assigned by XHCI controller) and invoke
> usb_hub_clear_tt_buffer() to send Clear_TT_Buffer request to the hub
> of the device for the following Set_Interface requests to the device
> 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)
> v4: Remove clearing_tt flag because hub_tt_work has hub->tt.lock
>     to protect for Clear_TT_Buffer to be run serially.
>     Remove xhci_clear_tt_buffer_complete as it's not necessary.
>     Same reason as the above.
>     Extend usb_hub_clear_tt_buffer parameter
> v5: Not extending usb_hub_clear_tt_buffer parameter
>     Add description.
> v6: Remove unused parameter slot_id from xhci_clear_hub_tt_buffer
> v7: Add devaddr field in "struct usb_device"
> v8: split as two patches
> v9: no change
> 
>  drivers/usb/host/xhci-ring.c | 12 ++++++++++++
>  drivers/usb/host/xhci.c      |  1 +
>  2 files changed, 13 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index 9215a28dad40..739737faf752 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -1786,6 +1786,17 @@ struct xhci_segment *trb_in_td(struct xhci_hcd *xhci,
>  	return NULL;
>  }
>  
> +static void xhci_clear_hub_tt_buffer(struct xhci_hcd *xhci, struct xhci_td *td)
> +{
> +	/*
> +	 * 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))
> +		usb_hub_clear_tt_buffer(td->urb);
> +}
> +
>  static void xhci_cleanup_halted_endpoint(struct xhci_hcd *xhci,
>  		unsigned int slot_id, unsigned int ep_index,
>  		unsigned int stream_id, struct xhci_td *td,
> @@ -1804,6 +1815,7 @@ static void xhci_cleanup_halted_endpoint(struct xhci_hcd *xhci,
>  	if (reset_type == EP_HARD_RESET) {
>  		ep->ep_state |= EP_HARD_CLEAR_TOGGLE;
>  		xhci_cleanup_stalled_ring(xhci, ep_index, stream_id, td);
> +		xhci_clear_hub_tt_buffer(xhci, td);
>  	}
>  	xhci_ring_cmd_db(xhci);
>  }

How come there's no clear_tt_buffer_complete() callback?  Without it,
xhci-hcd won't know when the TT buffer has been cleared, and so it
won't know when to restart the endpoint ring for the halted endpoint.  

Note: Restarting the endpoint ring before the TT buffer has been 
cleared is not safe.

Alan Stern

> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index 7fa58c99f126..68b393e5a453 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -4096,6 +4096,7 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
>  	/* Zero the input context control for later use */
>  	ctrl_ctx->add_flags = 0;
>  	ctrl_ctx->drop_flags = 0;
> +	udev->devaddr = (u8)(le32_to_cpu(slot_ctx->dev_state) & DEV_ADDR_MASK);
>  
>  	xhci_dbg_trace(xhci, trace_xhci_dbg_address,
>  		       "Internal device address = %d",
>