From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752992AbcHJXX1 (ORCPT ); Wed, 10 Aug 2016 19:23:27 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:48343 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752951AbcHJXXZ (ORCPT ); Wed, 10 Aug 2016 19:23:25 -0400 Date: Thu, 11 Aug 2016 00:22:58 +0100 From: Russell King - ARM Linux To: Laura Abbott Cc: Sumit Semwal , John Stultz , Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Riley Andrews , devel@driverdev.osuosl.org, Jon Medhurst , Android Kernel Team , Greg Kroah-Hartman , Daniel Vetter , Will Deacon , linux-kernel@vger.kernel.org, linaro-mm-sig@lists.linaro.org, Rohit kumar , Bryan Huntsman , Jeremy Gebben , Eun Taik Lee , Catalin Marinas , Liviu Dudau , Mitchel Humpherys , linux-arm-kernel@lists.infradead.org Subject: Re: [RFCv2][PATCH 2/5] arm: Implement ARCH_HAS_FORCE_CACHE Message-ID: <20160810232258.GQ1041@n2100.armlinux.org.uk> References: <1470678577-14010-1-git-send-email-labbott@redhat.com> <1470678577-14010-3-git-send-email-labbott@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1470678577-14010-3-git-send-email-labbott@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 08, 2016 at 10:49:34AM -0700, Laura Abbott wrote: > +/* > + * Make an area consistent for devices. > + * Note: Drivers should NOT use this function directly, as it will break > + * platforms with CONFIG_DMABOUNCE. > + * Use the driver DMA support - see dma-mapping.h (dma_sync_*) > + */ > +void __dma_page_cpu_to_dev(struct page *page, unsigned long off, > + size_t size, enum dma_data_direction dir) > +{ > + phys_addr_t paddr; > + > + dma_cache_maint_page(page, off, size, dir, dmac_map_area); > + > + paddr = page_to_phys(page) + off; > + if (dir == DMA_FROM_DEVICE) { > + outer_inv_range(paddr, paddr + size); > + } else { > + outer_clean_range(paddr, paddr + size); > + } > + /* FIXME: non-speculating: flush on bidirectional mappings? */ > +} > + > +void __dma_page_dev_to_cpu(struct page *page, unsigned long off, > + size_t size, enum dma_data_direction dir) > +{ > + phys_addr_t paddr = page_to_phys(page) + off; > + > + /* FIXME: non-speculating: not required */ > + /* in any case, don't bother invalidating if DMA to device */ > + if (dir != DMA_TO_DEVICE) { > + outer_inv_range(paddr, paddr + size); > + > + dma_cache_maint_page(page, off, size, dir, dmac_unmap_area); > + } > + > + /* > + * Mark the D-cache clean for these pages to avoid extra flushing. > + */ > + if (dir != DMA_TO_DEVICE && size >= PAGE_SIZE) { > + unsigned long pfn; > + size_t left = size; > + > + pfn = page_to_pfn(page) + off / PAGE_SIZE; > + off %= PAGE_SIZE; > + if (off) { > + pfn++; > + left -= PAGE_SIZE - off; > + } > + while (left >= PAGE_SIZE) { > + page = pfn_to_page(pfn++); > + set_bit(PG_dcache_clean, &page->flags); > + left -= PAGE_SIZE; > + } > + } > +} I _really_ don't want these exposed in any shape or form to driver code. I've seen too many hacks out there where people have gone under the cover of the APIs they should be using, and headed straight for the low-level functionality - adding function prototypes to get at stuff they have no business doing. Moving this here is just asking for it to be abused. > + > +void kernel_force_cache_clean(struct page *page, size_t size) > +{ > + __dma_page_cpu_to_dev(page, 0, size, DMA_BIDIRECTIONAL); > +} > + > +void kernel_force_cache_invalidate(struct page *page, size_t size) > +{ > + __dma_page_dev_to_cpu(page, 0, size, DMA_BIDIRECTIONAL); > +} Nothing in our implementation of these DMA operations guarantees that those mean "clean" and "invalidate". The DMA operations are there so that CPUs can implement whatever they need at the map and unmap times - and I've been very careful not to specify which cache operations are involved. For example, on older CPUs, __dma_page_dev_to_cpu() is almost always a no-op. If you want something that does something specific, then we need something designed to do something specific. Please don't re-use what you think will fit. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.