On Wed, Oct 4, 2023 at 5:03 PM Lad, Prabhakar <prabhakar.csengg@xxxxxxxxx> wrote: > > On Wed, Oct 4, 2023 at 3:18 PM Robin Murphy <robin.murphy@xxxxxxx> wrote: > > > > On 04/10/2023 3:02 pm, Icenowy Zheng wrote: > > [...] > > >>>> I believe commit 484861e09f3e ("soc: renesas: Kconfig: Select the > > >>>> required configs for RZ/Five SoC") can cause regression on all > > >>>> non-dma-coherent riscv platforms with generic defconfig. This is > > >>>> a common issue. The logic here is: generic riscv defconfig > > >>>> selects > > >>>> ARCH_R9A07G043 which selects DMA_GLOBAL_POOL, which assumes all > > >>>> non-dma-coherent riscv platforms have a dma global pool, this > > >>>> assumption > > >>>> seems not correct. And I believe DMA_GLOBAL_POOL should not be > > >>>> selected by ARCH_SOCFAMILIY, instead, only ARCH under some > > >>>> specific > > >>>> conditions can select it globaly, for example NOMMU ARM and so > > >>>> on. > > >>>> > > >>>> Since this is a regression, what's proper fix? any suggestion is > > >>>> appreciated. > > >> > > >> I think the answer is to not select DMA_GLOBAL_POOL, since that is > > >> only > > > > > > Well I think for RISC-V, it's not NOMMU only but applicable for every > > > core that does not support Svpbmt or vendor-specific alternatives, > > > because the original RISC-V priv spec does not define memory attributes > > > in page table entries. > > > > > > For the Renesas/Andes case I think a pool is set by OpenSBI with > > > vendor-specific M-mode facility and then passed in DT, and the S-mode > > > (which MMU is enabled in) just sees fixed memory attributes, in this > > > case I think DMA_GLOBAL_POOL is needed. > > > > Oh wow, is that really a thing? In that case, either you just can't > > support this platform in a multi-platform kernel, or someone needs to do > > some fiddly work in dma-direct to a) introduce the notion of an optional > > global pool, > Looking at the code [0] we do have compile time check for > CONFIG_DMA_GLOBAL_POOL irrespective of this being present in DT or > not, instead if we make it compile time and runtime check ie either > check for DT node or see if pool is available and only then proceed > for allocation form this pool. > > What are your thoughts on this? > Something like the below: diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h index f2fc203fb8a1..7bf41a4634a4 100644 --- a/include/linux/dma-map-ops.h +++ b/include/linux/dma-map-ops.h @@ -198,6 +198,7 @@ int dma_release_from_global_coherent(int order, void *vaddr); int dma_mmap_from_global_coherent(struct vm_area_struct *vma, void *cpu_addr, size_t size, int *ret); int dma_init_global_coherent(phys_addr_t phys_addr, size_t size); +bool dma_global_pool_available(void); #else static inline void *dma_alloc_from_global_coherent(struct device *dev, ssize_t size, dma_addr_t *dma_handle) @@ -213,6 +214,10 @@ static inline int dma_mmap_from_global_coherent(struct vm_area_struct *vma, { return 0; } +static inline bool dma_global_pool_available(void) +{ + return false; +} #endif /* CONFIG_DMA_GLOBAL_POOL */ /* diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c index c21abc77c53e..605f243b8262 100644 --- a/kernel/dma/coherent.c +++ b/kernel/dma/coherent.c @@ -277,6 +277,14 @@ int dma_mmap_from_dev_coherent(struct device *dev, struct vm_area_struct *vma, #ifdef CONFIG_DMA_GLOBAL_POOL static struct dma_coherent_mem *dma_coherent_default_memory __ro_after_init; +bool dma_global_pool_available(void) +{ + if (!dma_coherent_default_memory) + return false; + + return true; +} + void *dma_alloc_from_global_coherent(struct device *dev, ssize_t size, dma_addr_t *dma_handle) { diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index 9596ae1aa0da..a599bb731ceb 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -235,7 +235,7 @@ void *dma_direct_alloc(struct device *dev, size_t size, * If there is a global pool, always allocate from it for * non-coherent devices. */ - if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL)) + if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) && dma_global_pool_available()) return dma_alloc_from_global_coherent(dev, size, dma_handle); Cheers, Prabhakar > [0] https://elixir.bootlin.com/linux/v6.6-rc4/source/kernel/dma/direct.c#L238 > > > and b) make it somehow cope with DMA_DIRECT_REMAP being > > enabled but non-functional. > > > DMA_DIRECT_REMAP config option is selected by NONCOHERENET config option anyway. > > Cheers, > Prabhakar