Messages in this thread | | | Date | Fri, 2 Oct 2020 17:50:40 +0000 | From | Tomasz Figa <> | Subject | Re: [PATCH 8/8] WIP: add a dma_alloc_contiguous API |
| |
Hi Christoph,
On Wed, Sep 30, 2020 at 06:09:17PM +0200, Christoph Hellwig wrote: > Add a new API that returns a virtually non-contigous array of pages > and dma address. This API is only implemented for dma-iommu and will > not be implemented for non-iommu DMA API instances that have to allocate > contiguous memory. It is up to the caller to check if the API is > available.
Would you mind scheding some more light on what made the previous attempt not work well? I liked the previous API because it was more consistent with the regular dma_alloc_coherent().
> > The intent is that media drivers can use this API if either:
FWIW, the USB subsystem also has similar needs, and so do some DRM drivers using DMA API rather than IOMMU API directly. Basically I believe that all the users removed in your previous series relied on custom downstream patches to make DMA_ATTR_NON_CONSISTENT work and could be finally made work in upstream using this API.
> > - no kernel mapping or only temporary kernel mappings are required. > That is as a better replacement for DMA_ATTR_NO_KERNEL_MAPPING > - a kernel mapping is required for cached and DMA mapped pages, but > the driver also needs the pages to e.g. map them to userspace. > In that sense it is a replacement for some aspects of the recently > removed and never fully implemented DMA_ATTR_NON_CONSISTENT
What's the expected allocation and mapping flow with the latter? Would that be
pages = dma_alloc_noncoherent(...) vaddr = vmap(pages, ...);
?
Would one just use the usual dma_sync_for_{cpu,device}() for cache invallidate/clean, while keeping the mapping in place?
Best regards, Tomasz
| |