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The mt7621 SPI engine has a 32 byte buffer and the driver currently only allows 32-byte read requests and 36 bytes writes (there is a 4byte op/addr buffer). This is an unnecessary limitation. As the SPI clock is controlled by the host it is quite acceptable to send a larger message in multiple smaller transactions. As long as Chip Select is kept asserted the whole time, the SPI engine can be run multiple times for a single SPI message. This patch factors out the transaction logic and calls for each transfer in the message. A write transfer might leave bytes in the buffer to be combined with a following read transfer, as this is a common pattern. With this in place, we can remove the current max_transfer_size limit. In testing, this increases the read throughput for a NOR flash chip from 1.4MB/s to 2.3MB/s, a 50% improvement. Signed-off-by: NeilBrown <neil@brown.name> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.