On 26.09.2015 23:13, Steinar H. Gunderson wrote:
On Fri, Sep 25, 2015 at 10:12:51PM +0200, Steinar H. Gunderson wrote:
I have no idea whatsoever how this breaks bandwidth management, but seemingly
it does.
To verify; I built 4.3rc-2 with CONFIG_PM=n, and it can drive both cards
without problems whatwoever. So there's something about power management
(LPM?) in newer kernels that causes this issue.
Hi
Thanks again for taking the time to narrow down the issue.
Link power management (LPM) enabled for usb3 devices could be relevant because with LPM enabled the driver will
calculate a max exit latency time, the time it will will take to "wake up" a link from U1 or U2 to a fully running U0
Driver will tell the latency value to the host controller, when a exit latency time is set the host will know that
the link is power managed, and host will start to schedule additional PING TP transfers to the device to wake the link up to U0.
the PING TP tranfers are sent Max-exit-latency microeseconds before the actual transfer to make sure link is woken up in time.
It's possible that this impacts on the bandwidth.
It's also very possible that the max exit latency is calculated wrong, or that one of the other parameters set with the same
"evaluate context" command is wrong
-Mathias
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