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Prior to this patch, the bitmask ends up being 0x3, as opposed to 0x1 which likely was the intention. The erroneous bit results in the driver reporting 2 different button activations in designs with 2 or more buttons. To detect which button has been pressed, cyttsp5_btn_attention() uses a for loop to iterate through the input buffer, while shifting and applying a bitmask to determine the state for each button. Unfortunately, when the bitmask is 0x3 and there are multiple buttons, this procedure falls apart. Consider a design with 3 buttons. Pressing the third button will result in a call to cyttsp5_btn_attention() with the input buffer containing 0x4 (binary 0100). In the first iteration of the for loop cur_btn_state will be: (0x4 >> 0 * 1) & 0x3 = 0x4 & 0x3 = 0x0 This is correct. However, in the next iteration this happens: (0x4 >> 1 * 1) & 0x3 = 0x2 & 0x3 = 0x2 Which means that a key event for key 1 is generated, even though it's not really active. In the third iteration, the loop detects the button that was actually pressed: (0x4 >> 2 * 1) & 0x3 = 0x1 & 0x3 = 0x1 This key event is the only one that should have been detected, but it is accompanied by the preceding key. Ensuring the applied mask is 0x1 solves this problem. Signed-off-by: Richard Kjerstadius <richard.kjerstadius@teledyne.com> Reviewed-by: Alistair Francis <alistair@alistair23.me> Link: https://lore.kernel.org/r/20230127102903.3317089-1-richard.kjerstadius@teledyne.com Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com> |
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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.