* Robin Murphy <robin.murphy@xxxxxxx> [190226 23:36]: > On 2019-02-26 8:23 pm, Nicolin Chen wrote: > > This reverts commit d222e42e88168fd67e6d131984b86477af1fc256. > > > > The original change breaks omap dss: > > omapdss_dispc 58001000.dispc: > > dispc_errata_i734_wa_init: dma_alloc_writecombine failed > > > > Let's revert it first and then find a safer solution instead. Sounds like a good idea since we're only have few days left before the merge window. > Ah, I think I see the problem - once arch/arm's __dma_alloc() has decided to > use CMA (because dev_get_cma_area(dev) returns the global area), it then > won't fall back to trying a regular page allocation if > dma_alloc_from_contiguous() returns NULL. Thus anything on 32-bit Arm trying > to allocate a single-page buffer in blockable context with a CMA-enabled > config is just going to fail. Similarly, it looks like none of the > DMA_ATTR_FORCE_CONTIGUOUS cases are prepared to handle this change either > (amd_iommu appears technically affected, but is already using > dma_alloc_from_contiguous() backwards compared to everyone else, hmm). > > I guess the question is whether to add alloc_page()/free_page() fallbacks to > those call sites, or stuff them directly into the CMA helpers here. Well if you come up with some test patch, I can easily test it :) > > Would you please test and verify? Thanks! Yes this revert works for me: Tested-by: Tony Lindgren <tony@xxxxxxxxxxx>
