linux-kernel - Re: [PATCH v7 2/2] usb: new quirk to reduce the SET

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Message-ID: <7cbc1a70-2dcc-4a2a-99e6-fdd92bd5cc9b@rowland.harvard.edu>
Date:   Fri, 27 Oct 2023 11:49:13 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Hardik Gajjar <hgajjar@...adit-jv.com>
Cc:     gregkh@...uxfoundation.org, mathias.nyman@...el.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        erosca@...adit-jv.com, s.shtylyov@....ru
Subject: Re: [PATCH v7 2/2] usb: new quirk to reduce the SET_ADDRESS request
 timeout

On Fri, Oct 27, 2023 at 05:20:29PM +0200, Hardik Gajjar wrote:
> This patch introduces a new USB quirk,
> USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT, which modifies the timeout value
> for the SET_ADDRESS request. The standard timeout for USB request/command
> is 5000 ms, as recommended in the USB 3.2 specification (section 9.2.6.1).
> 
> However, certain scenarios, such as connecting devices through an APTIV
> hub, can lead to timeout errors when the device enumerates as full speed
> initially and later switches to high speed during chirp negotiation.
> 
> In such cases, USB analyzer logs reveal that the bus suspends for
> 5 seconds due to incorrect chirp parsing and resumes only after two
> consecutive timeout errors trigger a hub driver reset.
> 
> Packet(54) Dir(?) Full Speed J(997.100 us) Idle(  2.850 us)
> _______| Time Stamp(28 . 105 910 682)
> _______|_____________________________________________________________Ch0
> Packet(55) Dir(?) Full Speed J(997.118 us) Idle(  2.850 us)
> _______| Time Stamp(28 . 106 910 632)
> _______|_____________________________________________________________Ch0
> Packet(56) Dir(?) Full Speed J(399.650 us) Idle(222.582 us)
> _______| Time Stamp(28 . 107 910 600)
> _______|_____________________________________________________________Ch0
> Packet(57) Dir Chirp J( 23.955 ms) Idle(115.169 ms)
> _______| Time Stamp(28 . 108 532 832)
> _______|_____________________________________________________________Ch0
> Packet(58) Dir(?) Full Speed J (Suspend)( 5.347 sec) Idle(  5.366 us)
> _______| Time Stamp(28 . 247 657 600)
> _______|_____________________________________________________________Ch0
> 
> This 5-second delay in device enumeration is undesirable, particularly
> in automotive applications where quick enumeration is crucial
> (ideally within 3 seconds).
> 
> The newly introduced quirks provide the flexibility to align with a
> 3-second time limit, as required in specific contexts like automotive
> applications.
> 
> By reducing the SET_ADDRESS request timeout to 500 ms, the
> system can respond more swiftly to errors, initiate rapid recovery, and
> ensure efficient device enumeration. This change is vital for scenarios
> where rapid smartphone enumeration and screen projection are essential.
> 
> To use the quirk, please write "vendor_id:product_id:p" to
> /sys/bus/usb/drivers/hub/module/parameter/quirks
> 
> For example,
> echo "0x2c48:0x0132:p" > /sys/bus/usb/drivers/hub/module/parameters/quirks"
> 
> Signed-off-by: Hardik Gajjar <hgajjar@...adit-jv.com>
> ---

Reviewed-by: Alan Stern <stern@...land.harvard.edu>