Re: [PATCH 3/3] of: address: Use dma_default_coherent to determine default coherency
From: Robin Murphy <robin.murphy@arm.com>
Date: 2023-02-22 17:25:22
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linux-mips, linux-riscv, lkml
On 2023-02-22 13:37, Jiaxun Yang wrote:
As for now all arches have dma_default_coherent matched with default DMA coherency for of devices, so there is no need to have a standalone config option. This also fixes a case that for some MIPS platforms, coherency information is not carried in devicetree and kernel will override dma_default_coherent at early boot. Note for PowerPC: CONFIG_OF_DMA_DEFUALT_COHERENT was only selected when CONFIG_NOT_COHERENT_CACHE is false, in this case dma_default_coherent will be true, so it still matches present behavior. Note for RISC-V: dma_default_coherent is set to true at init code in this series.
OK, so the fundamental problem here is that we have two slightly different conflicting mechanisms, the ex-PowerPC config option, and the ex-MIPS dma_default_coherent for which of_dma_is_coherent() has apparently been broken forever. I'd agree that it's worth consolidating the two, but please separate out the fix as below, so it's feasible to backport without having to muck about in arch code.
quoted hunk ↗ jump to hunk
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com> --- arch/powerpc/Kconfig | 1 - arch/riscv/Kconfig | 1 - drivers/of/Kconfig | 4 ---- drivers/of/address.c | 2 +- 4 files changed, 1 insertion(+), 7 deletions(-)diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 2c9cdf1d8761..c67e5da714f7 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig@@ -272,7 +272,6 @@ config PPC select NEED_PER_CPU_PAGE_FIRST_CHUNK if PPC64 select NEED_SG_DMA_LENGTH select OF - select OF_DMA_DEFAULT_COHERENT if !NOT_COHERENT_CACHE select OF_EARLY_FLATTREE select OLD_SIGACTION if PPC32 select OLD_SIGSUSPENDdiff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 1d46a268ce16..406c6816d289 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig@@ -119,7 +119,6 @@ config RISCV select MODULES_USE_ELF_RELA if MODULES select MODULE_SECTIONS if MODULES select OF - select OF_DMA_DEFAULT_COHERENT select OF_EARLY_FLATTREE select OF_IRQ select PCI_DOMAINS_GENERIC if PCIdiff --git a/drivers/of/Kconfig b/drivers/of/Kconfig index 644386833a7b..e40f10bf2ba4 100644 --- a/drivers/of/Kconfig +++ b/drivers/of/Kconfig@@ -102,8 +102,4 @@ config OF_OVERLAY config OF_NUMA bool -config OF_DMA_DEFAULT_COHERENT - # arches should select this if DMA is coherent by default for OF devices - bool - endif # OFdiff --git a/drivers/of/address.c b/drivers/of/address.c index 4c0b169ef9bf..23ade4919853 100644 --- a/drivers/of/address.c +++ b/drivers/of/address.c@@ -1103,7 +1103,7 @@ phys_addr_t __init of_dma_get_max_cpu_address(struct device_node *np) bool of_dma_is_coherent(struct device_node *np) { struct device_node *node; - bool is_coherent = IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT); + bool is_coherent = dma_default_coherent;
AFAICS, all you should actually need is a single self-contained addition here, something like: + /* + * DT-based MIPS doesn't use OF_DMA_DEFAULT_COHERENT, but + * might override the system-wide default at runtime. + */ +#if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \ + defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \ + defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL) + is_coherent = dma_default_coherent; +#endif
node = of_node_get(np);
Then *after* that's fixed, we can do a more comprehensive refactoring to merge the two mechanisms properly. FWIW I think I'd prefer an approach closer to the first one, where config options control the initial value of dma_default_coherent rather than architectures having to override it unconditionally (and TBH I'd also like to have a generic config symbol for whether an arch supports per-device coherency or not). Thanks, Robin.