Messages in this thread | | | Date | Wed, 4 Oct 2023 20:38:39 +0100 | Subject | Re: [PATCH 0/6] RISC-V: Add eMMC support for TH1520 boards | From | Robin Murphy <> |
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On 2023-10-04 19:49, Samuel Holland wrote: > On 2023-10-04 12:16 PM, Lad, Prabhakar wrote: >> On Wed, Oct 4, 2023 at 5:03 PM Lad, Prabhakar >> <prabhakar.csengg@gmail.com> wrote: >>> >>> On Wed, Oct 4, 2023 at 3:18 PM Robin Murphy <robin.murphy@arm.com> 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); > > dma_alloc_from_global_coherent() already checks dma_coherent_default_memory, so > the solution could be even simpler: > > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -232,12 +232,12 @@ void *dma_direct_alloc(struct device *dev, size_t size, > attrs); > > /* > - * If there is a global pool, always allocate from it for > + * If there is a global pool, always try to allocate from it for > * non-coherent devices. > */ > - if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL)) > - return dma_alloc_from_global_coherent(dev, size, > - dma_handle); > + ret = dma_alloc_from_global_coherent(dev, size, dma_handle); > + if (ret) > + return ret;
So if allocation fails because the pool is full, we should go ahead and remap something that can't work? ;)
The dma_global_pool_available() idea sort of works, but I'm still concerned about the case where it *should* have been available but the platform has been misconfigured, so again we fall through to DMA_DIRECT_REMAP "successfully" returning a coherent buffer that isn't, and the user's filesystem gets corrupted. Or at best, they get confused by weird errors from random devices going wrong. That's why I said it would be fiddly - the current state of DMA_GLOBAL_POOL as a binary arch-wide thing is relatively robust and easy to reason about, but attempting to generalise it further is... less so.
Thanks, Robin.
> > /* > * Otherwise remap if the architecture is asking for it. But > > Regards, > Samuel >
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