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6423207e57
Aside from the synchronous Tx-Rx mode, which has been utilized to create the normal SPI transfers in the framework of the DW SSI driver, DW SPI controller supports Tx-only and EEPROM-read modes. The former one just enables the controller to transmit all the data from the Tx FIFO ignoring anything retrieved from the MISO lane. The later mode is so called write-then-read operation: DW SPI controller first pushes out all the data from the Tx FIFO, after that it'll automatically receive as much data as has been specified by means of the CTRLR1 register. Both of those modes can be used to implement the memory operations supported by the SPI-memory subsystem. The memory operation implementation is pretty much straightforward, except a few peculiarities we have had to take into account to make things working. Since DW SPI controller doesn't provide a way to directly set and clear the native CS lane level, but instead automatically de-asserts it when a transfer going on, we have to make sure the Tx FIFO isn't empty during entire Tx procedure. In addition we also need to read data from the Rx FIFO as fast as possible to prevent it' overflow with automatically fetched incoming traffic. The denoted peculiarities get to cause even more problems if DW SSI controller is equipped with relatively small FIFO and is connected to a relatively slow system bus (APB) (with respect to the SPI bus speed). In order to workaround the problems for as much as it's possible, the memory operation execution procedure collects all the Tx data into a single buffer and disables the local IRQs to speed the write-then-optionally-read method up. Note the provided memory operations are utilized by default only if a glue driver hasn't provided a custom version of ones and this is not a DW APB SSI controller with fixed automatic CS toggle functionality. Co-developed-by: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru> Signed-off-by: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> Link: https://lore.kernel.org/r/20201007235511.4935-18-Sergey.Semin@baikalelectronics.ru 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.