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Modern MIPS cores (like P5600/6600, M5150/6520, end so on) which got L2-cache on chip also can enable a special type Cache-Coherency attribute (CCA) named UnCached Accelerated attribute (UCA). In this way uncached accelerated accesses are treated the same way as non-accelerated uncached accesses, but uncached stores are gathered together for more efficient bus utilization. So to speak this CCA enables uncached transactions to better utilize bus bandwidth via burst transactions. This is exactly why ioremap_wc() method has been introduced in Linux. Alas MIPS-platform code hasn't implemented it so far, instead default one has been used which was an alias to ioremap_nocache. In order to fix this we added MIPS-specific ioremap_wc() macro substituted by generic __ioremap_mode() method call with writecombine CPU-info field passed. It shall create real ioremap_wc() method if CPU-cache supports UCA feature and fall-back to _CACHE_UNCACHED attribute if one doesn't. Additionally platform-specific io.h shall declare ARCH_HAS_IOREMAP_WC macro as indication of architectural definition of ioremap_wc() (similar to x86/powerpc). [paul.burton@mips.com: - Remove CC stable, this is new functionality.] Signed-off-by: Serge Semin <fancer.lancer@gmail.com> Signed-off-by: Paul Burton <paul.burton@mips.com> Patchwork: https://patchwork.linux-mips.org/patch/19789/ Cc: James Hogan <jhogan@kernel.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: linux-mips@linux-mips.org Cc: okaya@codeaurora.org Cc: chenhc@lemote.com Cc: Sergey.Semin@t-platforms.ru Cc: linux-kernel@vger.kernel.org |
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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.
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.