Greg? On 08/06/17 17:25, Russell King - ARM Linux wrote: > Well, I've no objection to this, but it does need acks from other > people before I can apply it. > > There's two patches that touch drivers/base that need Greg's ack. > > I'm not sure what's happening with lib/dma-noop.c, there doesn't > appear to be a maintainer list for it, so I guess that's a > free-for-all. > > On Thu, Jun 08, 2017 at 09:28:30AM +0100, Vladimir Murzin wrote: >> Ping! >> >> On 24/05/17 11:24, Vladimir Murzin wrote: >>> Short story: >>> >>> Without these patches coherent DMA is broken for András and Alexandre, >>> so they cannot safely enable DMA on their platforms. >>> >>> Patches have been circulated on a list since last year without much >>> attention to changes in dma-coherent.c and dma-noop.c. Meanwhile, ARM >>> bits have been reviewed and there is no strict objection to get them >>> merged. Unfortunately, applying only ARM bits doesn't help much and >>> the original issue would still exist. >>> >>> Please, let me know how to move with this fix forward? >>> >>> Long story: >>> >>> It seems that addition of cache support for M-class CPUs uncovered >>> latent bug in DMA usage. NOMMU memory model has been treated as being >>> always consistent; however, for R/M CPU classes memory can be covered >>> by MPU which in turn might configure RAM as Normal i.e. bufferable and >>> cacheable. It breaks dma_alloc_coherent() and friends, since data can >>> stuck in caches now or be buffered. >>> >>> This patch set is trying to address the issue by providing region of >>> memory suitable for consistent DMA operations. It is supposed that >>> such region is marked by MPU as non-cacheable. Robin suggested to >>> advertise such memory as reserved shared-dma-pool, rather then using >>> homebrew command line option, and extend dma-coherent to provide >>> default DMA area in the similar way as it is done for CMA (PATCH >>> 4/7). It allows us to offload all bookkeeping on generic coherent DMA >>> framework, and it seems that it might be reused by other architectures >>> like c6x and blackfin. >>> >>> While reviewing/testing previous versions of the patch set it turned >>> out that dma-coherent does not take into account "dma-ranges" device >>> tree property, so it is addressed in PATCH 3/7. >>> >>> For ARM, dedicated DMA region is required for cases other than: >>> - MMU/MPU is off >>> - cpu is v7m w/o cache support >>> - device is coherent >>> >>> In case any of the above conditions is true dma operations are forced >>> to be coherent and wired with dma_noop_ops. >>> >>> To make life easier NOMMU dma operations are kept in separate >>> compilation unit. >>> >>> Since the issue was reported at the same time as Benjamin sent his >>> patch [1] to allow mmap for NOMMU, his case is also addressed in this >>> series (PATCH 1/7 and PATCH 2/7). >>> >>> Thanks! >>> >>> [1] http://www.armlinux.org.uk/developer/patches/viewpatch.php?id=8633/1 >>> >>> Cc: Joerg Roedel <jroe...@suse.de> >>> Cc: Christian Borntraeger <borntrae...@de.ibm.com> >>> Cc: Michal Nazarewicz <min...@mina86.com> >>> Cc: Marek Szyprowski <m.szyprow...@samsung.com> >>> Cc: Alan Stern <st...@rowland.harvard.edu> >>> Cc: Yoshinori Sato <ys...@users.sourceforge.jp> >>> Cc: Rich Felker <dal...@libc.org> >>> Cc: Roger Quadros <rog...@ti.com> >>> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> >>> Cc: Rob Herring <robh...@kernel.org> >>> Cc: Mark Rutland <mark.rutl...@arm.com> >>> Cc: Doug Ledford <dledf...@redhat.com> >>> >>> Changelog: >>> v4 -> v5 >>> - rebased on v4.12-rc2 >>> - updated description for CONFIG_ARM_DMA_MEM_BUFFERABLE >>> >>> v3 -> v4 >>> - rebased on v4.11-rc7 >>> - made CONFIG_ARM_DMA_MEM_BUFFERABLE optional for CPU_V7M >>> - added Arnd's Acked-by >>> >>> v2 -> v3 >>> - fixed warnings reported by Alexandre and kbuild robot >>> >>> v1 -> v2 >>> - rebased on v4.11-rc1 >>> - added Robin's Reviewed-by >>> - dedicated flag is introduced to use dev->dma_pfn_offset >>> rather than mem->device_base in case memory region is >>> configured via device tree (so Tested-by discarded there) >>> >>> RFC v6 -> v1 >>> - dropped RFC tag >>> - added Alexandre's Tested-by >>> >>> Vladimir Murzin (7): >>> dma: Take into account dma_pfn_offset >>> dma: Add simple dma_noop_mmap >>> drivers: dma-coherent: Account dma_pfn_offset when used with device >>> tree >>> drivers: dma-coherent: Introduce default DMA pool >>> ARM: NOMMU: Introduce dma operations for noMMU >>> ARM: NOMMU: Set ARM_DMA_MEM_BUFFERABLE for M-class cpus >>> ARM: dma-mapping: Remove traces of NOMMU code >>> >>> .../bindings/reserved-memory/reserved-memory.txt | 3 + >>> arch/arm/Kconfig | 1 + >>> arch/arm/include/asm/dma-mapping.h | 2 +- >>> arch/arm/mm/Kconfig | 8 +- >>> arch/arm/mm/Makefile | 5 +- >>> arch/arm/mm/dma-mapping-nommu.c | 253 >>> +++++++++++++++++++++ >>> arch/arm/mm/dma-mapping.c | 29 +-- >>> drivers/base/dma-coherent.c | 74 +++++- >>> lib/dma-noop.c | 29 ++- >>> 9 files changed, 359 insertions(+), 45 deletions(-) >>> create mode 100644 arch/arm/mm/dma-mapping-nommu.c >>> >> >
