> 2023年2月22日 16:02，Conor Dooley <conor@xxxxxxxxxx> 写道： > > 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? Hmm that sounds like a good idea but I was unable to find a place for this. riscv/mm/dma-noncoherent.c are just a bunch of callbacks, there is no initialisation function that will always run on every boot. riscv_noncoherent_supported is only called conditionally. Perhaps I can add a initcall in dma-noncoherent.c but it seems to be a little bit overkilling. Actually I’d prefer to have a config option for the default value but it seems like it’s not in Christoph’s flavour. Thanks - Jiaxun
