On Mon, Mar 27, 2023 at 02:13:16PM +0200, Arnd Bergmann wrote: > From: Arnd Bergmann <arnd@xxxxxxxx> > > The arm version of the arch_sync_dma_for_cpu() function annotates pages as > PG_dcache_clean after a DMA, but no other architecture does this here. ... because this is an arm32 specific feature. Generically, it's PG_arch_1, which is a page flag free for architecture use. On arm32 we decided to use this to mark whether we can skip dcache writebacks when establishing a PTE - and thus it was decided to call it PG_dcache_clean to reflect how arm32 decided to use that bit. This isn't just a DMA thing, there are other places that we update the bit, such as flush_dcache_page() and copy_user_highpage(). So thinking that the arm32 PG_dcache_clean is something for DMA is actually wrong. Other architectures are free to do their own other optimisations using that bit, and their implementations may be DMA-centric. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
