On 11/14/2018 3:30 AM, Doug Anderson wrote:
Hi,
On Sun, Sep 9, 2018 at 9:24 PM Terin Stock terin@terinstock.com wrote:
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: 11977After 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: 1002The floppy drive operates properly with delays up to approximately 5ms, and sends NAKs for any delays that are longer.
Fixes: 38d2b5fb75c1 ("usb: dwc2: host: Don't retry NAKed transactions right away") Signed-off-by: Terin Stock terin@terinstock.com
drivers/usb/dwc2/hcd.h | 2 +- drivers/usb/dwc2/hcd_queue.c | 19 ++++++++++++------- 2 files changed, 13 insertions(+), 8 deletions(-)
Reviewed-by: Douglas Anderson dianders@chromium.org Cc: stable@vger.kernel.org
Acked-by: Minas Harutyunyan hminas@synopsys.com