On Wed, Feb 22, 2023 at 03:55:19PM +0000, Jiaxun Yang wrote: > > > > 2023年2月22日 14:50，Conor Dooley <conor@xxxxxxxxxx> 写道： > > > > On Wed, Feb 22, 2023 at 01:37:11PM +0000, Jiaxun Yang wrote: > >> For riscv our assumption is unless a device states it is non-coherent, > >> we take it to be DMA coherent. > >> > >> For devicetree probed devices that have been true since very begining > >> with OF_DMA_DEFAULT_COHERENT selected. > >> > >> Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> > >> --- > >> arch/riscv/kernel/setup.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > >> index 376d2827e736..34b371180976 100644 > >> --- a/arch/riscv/kernel/setup.c > >> +++ b/arch/riscv/kernel/setup.c > >> @@ -300,6 +300,9 @@ void __init setup_arch(char **cmdline_p) > >> riscv_init_cbom_blocksize(); > >> riscv_fill_hwcap(); > >> apply_boot_alternatives(); > >> +#ifdef CONFIG_RISCV_DMA_NONCOHERENT > >> + dma_default_coherent = true; > >> +#endif > > > > Do we really need to add ifdeffery for this here? > > It's always coherent by default, so why do we need to say set it in > > setup_arch() when we know that, regardless of options, it is true? > > Because this symbol is only a variable when: > > 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) > > Which is only true if CONFIG_RISCV_DMA_NONCOHERENT is selected. > > Otherwise this symbol is defined to true and we can’t make a assignment to it. Maybe I am just slow today, but I don't get why you need to add ifdeffery to setup_arch() to do something that is always true. Why can't you just set this in riscv/mm/dma-noncoherent.c? What am I missing? Cheers, Conor. > >> if (IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM) && > >> riscv_isa_extension_available(NULL, ZICBOM)) > >> riscv_noncoherent_supported(); > >> -- > >> 2.37.1 (Apple Git-137.1) > >
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