On Wed, Feb 22, 2023 at 03:55:19PM +0000, Jiaxun Yang wrote:

quoted

2023年2月22日 14:50，Conor Dooley [off-list ref] 写道：

On Wed, Feb 22, 2023 at 01:37:11PM +0000, Jiaxun Yang wrote:

quoted

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@flygoat.com>
---
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.

quoted

quoted

if (IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM) &&
    riscv_isa_extension_available(NULL, ZICBOM))
riscv_noncoherent_supported();
-- 
2.37.1 (Apple Git-137.1)