Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
a2035411fa
USB 3.x SuperSpeed peripherals can draw up to 900mA of VBUS power when in configured state. However, if a configuration wanting to take advantage of this is added with MaxPower greater than 500 (currently possible if using a ConfigFS gadget) the composite driver fails to accommodate this for a couple reasons: - usb_gadget_vbus_draw() when called from set_config() and composite_resume() will be passed the MaxPower value without regard for the current connection speed, resulting in a violation for USB 2.0 since the max is 500mA. - the bMaxPower of the configuration descriptor would be incorrectly encoded, again if the connection speed is only at USB 2.0 or below, likely wrapping around U8_MAX since the 2mA multiplier corresponds to a maximum of 510mA. Fix these by adding checks against the current gadget->speed when the c->MaxPower value is used (set_config() and composite_resume()) and appropriately limit based on whether it is currently at a low-/full-/high- or super-speed connection. Because 900 is not divisible by 8, with the round-up division currently used in encode_bMaxPower() a MaxPower of 900mA will result in an encoded value of 0x71. When a host stack (including Linux and Windows) enumerates this on a single port root hub, it reads this value back and decodes (multiplies by 8) to get 904mA which is strictly greater than 900mA that is typically budgeted for that port, causing it to reject the configuration. Instead, we should be using the round-down behavior of normal integral division so that 900 / 8 -> 0x70 or 896mA to stay within range. And we might as well change it for the high/full/low case as well for consistency. N.B. USB 3.2 Gen N x 2 allows for up to 1500mA but there doesn't seem to be any any peripheral controller supported by Linux that does two lane operation, so for now keeping the clamp at 900 should be fine. Signed-off-by: Jack Pham <jackp@codeaurora.org> Signed-off-by: Felipe Balbi <balbi@kernel.org> |
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README
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.
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.