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CONFIG_ARCH_WRITECOMBINE: Enable WriteCombine (WUC) for ioremap()

General informations

The Linux kernel configuration item CONFIG_ARCH_WRITECOMBINE:

Help text

LoongArch maintains cache coherency in hardware, but when paired with LS7A chipsets the WUC attribute (Weak-ordered UnCached, which is similar to WriteCombine) is out of the scope of cache coherency machanism for PCIe devices (this is a PCIe protocol violation, which may be fixed in newer chipsets).

This means WUC can only used for write-only memory regions now, so this option is disabled by default, making WUC silently fallback to SUC for ioremap(). You can enable this option if the kernel is ensured to run on hardware without this bug.

You can override this setting via writecombine=on/off boot parameter.



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