From db91427b6502e8e46db4b616e4eaa9b9cf4e6363 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Mon, 26 Aug 2019 09:22:13 +0200 Subject: [PATCH] MIPS: document mixing "slightly different CCAs" Based on an email from Paul Burton, quoting section 4.8 "Cacheability and Coherency Attributes and Access Types" of "MIPS Architecture Volume 1: Introduction to the MIPS32 Architecture" (MD00080, revision 6.01). Signed-off-by: Christoph Hellwig Acked-by: Paul Burton --- arch/mips/Kconfig | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index fc88f68ea1ee..aff1cadeea43 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -1119,6 +1119,13 @@ config DMA_PERDEV_COHERENT config DMA_NONCOHERENT bool + # + # MIPS allows mixing "slightly different" Cacheability and Coherency + # Attribute bits. It is believed that the uncached access through + # KSEG1 and the implementation specific "uncached accelerated" used + # by pgprot_writcombine can be mixed, and the latter sometimes provides + # significant advantages. + # select ARCH_HAS_DMA_WRITE_COMBINE select ARCH_HAS_SYNC_DMA_FOR_DEVICE select ARCH_HAS_UNCACHED_SEGMENT -- 2.30.2