> 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. Thanks - Jiaxun > > 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)
