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The Synopsis DesignWare DW_apb_ssi specifications version 3.23 onward define a 32-bits maximum transfer size synthesis parameter (SSI_MAX_XFER_SIZE=32) in addition to the legacy 16-bits configuration (SSI_MAX_XFER_SIZE=16) for SPI controllers. When SSI_MAX_XFER_SIZE=32, the layout of the ctrlr0 register changes, moving the data frame format field from bits [3..0] to bits [16..20], and the RX/TX FIFO word size can be up to 32-bits. To support this new format, introduce the DW SPI capability flag DW_SPI_CAP_DFS32 to indicate that a controller is configured with SSI_MAX_XFER_SIZE=32. Since SSI_MAX_XFER_SIZE is a controller synthesis parameter not accessible through a register, the detection of this parameter value is done in spi_hw_init() by writing and reading the ctrlr0 register and testing the value of bits [3..0]. These bits are ignored (unchanged) for SSI_MAX_XFER_SIZE=16, allowing the detection. If a DFS32 capable SPI controller is detected, the new field dfs_offset in struct dw_spi is set to SPI_DFS32_OFFSET (16). dw_spi_update_config() is modified to set the data frame size field at the correct position is the CTRLR0 register, as indicated by the dfs_offset field of the dw_spi structure. The DW_SPI_CAP_DFS32 flag is also unconditionally set for SPI slave controllers, e.g. controllers that have the DW_SPI_CAP_DWC_SSI capability flag set. However, for these ssi controllers, the dfs_offset field is set to 0 as before (as per specifications). Finally, for any controller with the DW_SPI_CAP_DFS32 capability flag set, dw_spi_add_host() extends the value of bits_per_word_mask from 16-bits to 32-bits. dw_reader() and dw_writer() are also modified to handle 32-bits iTX/RX FIFO words. Suggested-by: Sean Anderson <seanga2@gmail.com> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Acked-by: Serge Semin <fancer.lancer@gmail.com> Link: https://lore.kernel.org/r/20201206011817.11700-3-damien.lemoal@wdc.com Signed-off-by: Mark Brown <broonie@kernel.org> |
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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.