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commit6ed30a7d8eupstream. Modify the wait delay utilize the high resolution timer API to allow for more precisely scheduled callbacks. A previous commit added a 1ms retry delay after multiple consecutive NAKed transactions using jiffies. On systems with a low timer interrupt frequency, this delay may be significantly longer than specified, resulting in misbehavior with some USB devices. This scenario was reached on a Raspberry Pi 3B with a Macally FDD-USB floppy drive (identified as 0424:0fdc Standard Microsystems Corp. Floppy, based on the USB97CFDC USB FDC). With the relay delay, the drive would be unable to mount a disk, replying with NAKs until the device was reset. Using ktime, the delta between starting the timer (in dwc2_hcd_qh_add) and the callback function can be determined. With the original delay implementation, this value was consistently approximately 12ms. (output in us). <idle>-0 [000] ..s. 1600.559974: dwc2_wait_timer_fn: wait_timer delta: 11976 <idle>-0 [000] ..s. 1600.571974: dwc2_wait_timer_fn: wait_timer delta: 11977 <idle>-0 [000] ..s. 1600.583974: dwc2_wait_timer_fn: wait_timer delta: 11976 <idle>-0 [000] ..s. 1600.595974: dwc2_wait_timer_fn: wait_timer delta: 11977 After converting the relay delay to using a higher resolution timer, the delay was much closer to 1ms. <idle>-0 [000] d.h. 1956.553017: dwc2_wait_timer_fn: wait_timer delta: 1002 <idle>-0 [000] d.h. 1956.554114: dwc2_wait_timer_fn: wait_timer delta: 1002 <idle>-0 [000] d.h. 1957.542660: dwc2_wait_timer_fn: wait_timer delta: 1004 <idle>-0 [000] d.h. 1957.543701: dwc2_wait_timer_fn: wait_timer delta: 1002 The floppy drive operates properly with delays up to approximately 5ms, and sends NAKs for any delays that are longer. Fixes:38d2b5fb75("usb: dwc2: host: Don't retry NAKed transactions right away") Cc: <stable@vger.kernel.org> Reviewed-by: Douglas Anderson <dianders@chromium.org> Acked-by: Minas Harutyunyan <hminas@synopsys.com> Signed-off-by: Terin Stock <terin@terinstock.com> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.