Messages in this thread | | | Subject | Re: [PATCH] dma-pool: Do not allocate pool memory from CMA | From | Nicolas Saenz Julienne <> | Date | Tue, 28 Jul 2020 11:30:32 +0200 |
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On Tue, 2020-07-28 at 11:13 +0200, Christoph Hellwig wrote: > On Mon, Jul 27, 2020 at 07:56:56PM +0200, Nicolas Saenz Julienne wrote: > > Hi Christoph, > > thanks for having a look at this! > > > > On Fri, 2020-07-24 at 15:41 +0200, Christoph Hellwig wrote: > > > Yes, the iommu is an interesting case, and the current code is > > > wrong for that. > > > > Care to expand on this? I do get that checking dma_coherent_ok() on memory > > that'll later on be mapped into an iommu is kind of silly, although I think > > harmless in Amir's specific case, since devices have wide enough dma- ranges. > > Is > > there more to it? > > I think the problem is that it can lead to not finding suitable memory. > > > > Can you try the patch below? It contains a modified version of Nicolas' > > > patch to try CMA again for the expansion and a new (for now hackish) way > > > to > > > not apply the addressability check for dma-iommu allocations. > > > > > > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c > > > index 6bc74a2d51273e..ec5e525d2b9309 100644 > > > --- a/kernel/dma/pool.c > > > +++ b/kernel/dma/pool.c > > > @@ -3,7 +3,9 @@ > > > * Copyright (C) 2012 ARM Ltd. > > > * Copyright (C) 2020 Google LLC > > > */ > > > +#include <linux/cma.h> > > > #include <linux/debugfs.h> > > > +#include <linux/dma-contiguous.h> > > > #include <linux/dma-direct.h> > > > #include <linux/dma-noncoherent.h> > > > #include <linux/init.h> > > > @@ -55,6 +57,31 @@ static void dma_atomic_pool_size_add(gfp_t gfp, size_t > > > size) > > > pool_size_kernel += size; > > > } > > > > > > +static bool cma_in_zone(gfp_t gfp) > > > +{ > > > + phys_addr_t end; > > > + unsigned long size; > > > + struct cma *cma; > > > + > > > + cma = dev_get_cma_area(NULL); > > > + if (!cma) > > > + return false; > > > + > > > + size = cma_get_size(cma); > > > + if (!size) > > > + return false; > > > + end = cma_get_base(cma) - memblock_start_of_DRAM() + size - 1; > > > + > > > + /* CMA can't cross zone boundaries, see cma_activate_area() */ > > > + if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp & GFP_DMA) && > > > + end <= DMA_BIT_MASK(zone_dma_bits)) > > > + return true; > > > + if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32) && > > > + end <= DMA_BIT_MASK(32)) > > > + return true; > > > + return true; > > > > IIUC this will always return true given a CMA is present. Which reverts to > > the > > previous behaviour (previous as in breaking some rpi4 setups), isn't it? > > Was that really what broke the PI? I'll try to get the split out series > today, which might have a few more tweaks, and then we'll need to test it > both on these rpi4 setups and Amits phone.
There was two issues with RPi: - Not validating that pool allocated memory was OK for the device - Locating all atomic pools in CMA, which doesn't work for all RPi4 devices*, and IMO misses the point of having multiple pools.
* With ACPI RPi4 we have CMA located in ZONE_DMA32, yet have an atomic pool consumer, PCIe, that only wants memory in the [0 3GB] area, effectively needing ZONE_DMA memory.
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