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According to USB 2.0 Spec Table 7-7, the High-speed squelch detection threshold Min 100mV and Max 150mV, and we set USB 2.0 PHY0 and PHY1 squelch detection threshold to 150mV by default, so if the amplitude of differential voltage envelope is < 150 mV, the USB 2.0 PHYs envelope detector will indicate it as squelch. On RK3399 box, if we connect usb device with a 4 meter cable, we can see that the impedance of U2 cable is too big according to the eye-diagram test report, and this cause serious signal attenuation at the end of receiver, the amplitude of differential voltage falls below 150mV. This patch aims to reduce the PHY0 and PHY1 otg-ports squelch detection threshold to 125mV (host-ports still use 150mV by default), this is helpful to increase USB 2.0 PHY compatibility. Change-Id: Iec8b4043a3440d6f2a5fb18ff59ac0f4988019e9 Signed-off-by: Meng Dongyang <daniel.meng@rock-chips.com> Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
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.