On 2023-02-22 13:37, Jiaxun Yang wrote:
As for now all arches have dma_default_coherent matched with default
DMA coherency for of devices, so there is no need to have a standalone
config option.
This also fixes a case that for some MIPS platforms, coherency information
is not carried in devicetree and kernel will override dma_default_coherent
at early boot.
Note for PowerPC: CONFIG_OF_DMA_DEFUALT_COHERENT was only selected when
CONFIG_NOT_COHERENT_CACHE is false, in this case dma_default_coherent will
be true, so it still matches present behavior.
Note for RISC-V: dma_default_coherent is set to true at init code in this
series.
OK, so the fundamental problem here is that we have two slightly
different conflicting mechanisms, the ex-PowerPC config option, and the
ex-MIPS dma_default_coherent for which of_dma_is_coherent() has
apparently been broken forever.
I'd agree that it's worth consolidating the two, but please separate out
the fix as below, so it's feasible to backport without having to muck
about in arch code.
Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
---
arch/powerpc/Kconfig | 1 -
arch/riscv/Kconfig | 1 -
drivers/of/Kconfig | 4 ----
drivers/of/address.c | 2 +-
4 files changed, 1 insertion(+), 7 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2c9cdf1d8761..c67e5da714f7 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -272,7 +272,6 @@ config PPC
select NEED_PER_CPU_PAGE_FIRST_CHUNK if PPC64
select NEED_SG_DMA_LENGTH
select OF
- select OF_DMA_DEFAULT_COHERENT if !NOT_COHERENT_CACHE
select OF_EARLY_FLATTREE
select OLD_SIGACTION if PPC32
select OLD_SIGSUSPEND
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 1d46a268ce16..406c6816d289 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -119,7 +119,6 @@ config RISCV
select MODULES_USE_ELF_RELA if MODULES
select MODULE_SECTIONS if MODULES
select OF
- select OF_DMA_DEFAULT_COHERENT
select OF_EARLY_FLATTREE
select OF_IRQ
select PCI_DOMAINS_GENERIC if PCI
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index 644386833a7b..e40f10bf2ba4 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -102,8 +102,4 @@ config OF_OVERLAY
config OF_NUMA
bool
-config OF_DMA_DEFAULT_COHERENT
- # arches should select this if DMA is coherent by default for OF devices
- bool
-
endif # OF
diff --git a/drivers/of/address.c b/drivers/of/address.c
index 4c0b169ef9bf..23ade4919853 100644
--- a/drivers/of/address.c
+++ b/drivers/of/address.c
@@ -1103,7 +1103,7 @@ phys_addr_t __init of_dma_get_max_cpu_address(struct device_node *np)
bool of_dma_is_coherent(struct device_node *np)
{
struct device_node *node;
- bool is_coherent = IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT);
+ bool is_coherent = dma_default_coherent;
AFAICS, all you should actually need is a single self-contained addition
here, something like:
+ /*
+ * DT-based MIPS doesn't use OF_DMA_DEFAULT_COHERENT, but
+ * might override the system-wide default at runtime.
+ */
+#if 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)
+ is_coherent = dma_default_coherent;
+#endif
node = of_node_get(np);
Then *after* that's fixed, we can do a more comprehensive refactoring to
merge the two mechanisms properly. FWIW I think I'd prefer an approach
closer to the first one, where config options control the initial value
of dma_default_coherent rather than architectures having to override it
unconditionally (and TBH I'd also like to have a generic config symbol
for whether an arch supports per-device coherency or not).
Thanks,
Robin.
