On 01.03.2018 13:56, Greg KH wrote:
On Thu, Mar 01, 2018 at 01:15:28PM +0200, Mathias Nyman wrote:
Disabing Latency Tolerance Messaging before port reset is unnecessary.
LTM is automatically disabled at port reset.
If host can't communicate with the device the LTM message will fail, and
the hub driver will unnecessarily do a logical disconnect.
Broken communication is ofter the reason for a reset in the first place.
Additionally we can't guarantee device is in a configured state,
epecially in reset-resume case when root hub lost power.
LTM can't be modified unless device is in a configured state.
Just remove LTM disabling before port reset.
Details about LTM and port reset in USB 3 specification:
USB 3 spec section 9.4.5
"The LTM Enable field can be modified by the SetFeature() and
ClearFeature() requests using the LTM_ENABLE feature selector.
This field is reset to zero when the device is reset."
USB 3 spec section 9.4.1
"The device shall process a Clear Feature (U1_Enable or U2_Enable or
LTM_Enable) only if the device is in the configured state."
Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
---
drivers/usb/core/hub.c | 12 +++---------
1 file changed, 3 insertions(+), 9 deletions(-)
Is this causing problems now such that we should get this to older
kernels as well?
Could be, it can reduce extra logical disconnects on reset on resume.
But this didn't resolve some some real life bug, it was one thing Alan commented on
while debugging a failing USB3 device reset.
-Mathias
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