On Wed, Feb 22, 2023 at 04:20:16PM +0000, Jiaxun Yang wrote: > > 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. Right, that's fair. riscv_noncoherent_supported() is for when we know we can support non-coherent DMA, not to detect whether we can, hence the conditional nature. Apologies for sending you on a wild goose chase there. > Perhaps I can add a initcall in dma-noncoherent.c but it seems to be a little bit > overkilling. Yah, probably would be. > Actually I’d prefer to have a config option for the default value but it seems like > it’s not in Christoph’s flavour. We already have a config option that sets things up nicely for RISC-V that you're getting rid of! ;)
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