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The Transfer Complete Flag (TCF) interrupt gets raised after each write to the TX FIFO (PUSHR) which means that it is not possible to devise a transfer procedure that makes full utilization of the FIFO depth (4 entries on most controllers, 16 entries on some). On the other hand, XSPI mode has a feature called "command cycling", which allows a single TX command to be run for a pre-specified number of TX words. When the command cycle ends, the Command Transfer Complete Flag bit asserts and raises an interrupt. The advantage in this mode is that the TX FIFO can be better utilized (more words can be batched at once). Other changes brought by this patch: - The dspi->rx_end variable has been removed, since now the dspi_fifo_write function sets up dspi->words_in_flight, so dspi_fifo_read knows how much to read without overrunning the RX buffer. - Stop using poll mode unconditionally for TCFQ mode, since XSPI mode is a little less efficient than that, and so, poll mode doesn't bring as many improvements for XSPI. - Stop relying on the hardware transfer counter (SPI_TCR_GET_TCNT) and instead increment the message->actual_length based on the newly introduced dspi->words_in_flight variable. - The CTARE register is now written in the hotpath instead of just at transfer init time, since it contains the DTCP field (transfer preload - the counter indicating how many txdata words will follow), which is a dynamic value. Due to the fact that the Chip Select toggling setting is part of the command written to the TX FIFO, the ending word of each buffer needs to be sent via its own TX command, so that we have a chance to emit a 1-word command with deasserted PCS. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Link: https://lore.kernel.org/r/20200304220044.11193-9-olteanv@gmail.com Signed-off-by: Mark Brown <broonie@kernel.org> |
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
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| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| Makefile | ||
| 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.