Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
bcf41dc480
Some of the chips supported by the pca953x driver need the most significant bit in the address word set to automatically increment the address pointer on subsequent reads and writes (example: PCA9505). With this bit unset the same register is read multiple times on a multi-byte read sequence. Other chips must not have this bit set and autoincrement always (example: PCA9555). Up to now this AI bit was interpreted to be part of the address, which resulted in inconsistent regmap caching when a register was written with AI set and then read without it. This happened for the PCA9505 in pca953x_gpio_set_multiple() where pca953x_read_regs() bulk read from the cache for registers 0x8-0xc and then wrote to registers 0x88-0x8c. (Side note: reading 5 values from offset 0x8 yiels OP0 5 times because AI must be set to get OP0-OP4, which is another bug that is resolved here as a by-product.) The same problem happens when calls to gpio_set_value() and gpio_set_array_value() were mixed. With this patch the AI bit is always set for chips that support it. This works as there are no code locations that make use of the behaviour with AI unset (for the chips that support it). Note that the call to pca953x_setup_gpio() had to be done a bit earlier to make the NBANK macro work. The history of this bug is a bit complicated. Commit |
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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.