On 04/10/2023 3:02 pm, Icenowy Zheng wrote:
[...]
I believe commit 484861e09f3e ("soc: renesas: Kconfig: Select the
required configs for RZ/Five SoC") can cause regression on all
non-dma-coherent riscv platforms with generic defconfig. This is
a common issue. The logic here is: generic riscv defconfig
selects
ARCH_R9A07G043 which selects DMA_GLOBAL_POOL, which assumes all
non-dma-coherent riscv platforms have a dma global pool, this
assumption
seems not correct. And I believe DMA_GLOBAL_POOL should not be
selected by ARCH_SOCFAMILIY, instead, only ARCH under some
specific
conditions can select it globaly, for example NOMMU ARM and so
on.
Since this is a regression, what's proper fix? any suggestion is
appreciated.
I think the answer is to not select DMA_GLOBAL_POOL, since that is
only
Well I think for RISC-V, it's not NOMMU only but applicable for every
core that does not support Svpbmt or vendor-specific alternatives,
because the original RISC-V priv spec does not define memory attributes
in page table entries.
For the Renesas/Andes case I think a pool is set by OpenSBI with
vendor-specific M-mode facility and then passed in DT, and the S-mode
(which MMU is enabled in) just sees fixed memory attributes, in this
case I think DMA_GLOBAL_POOL is needed.
Oh wow, is that really a thing? In that case, either you just can't
support this platform in a multi-platform kernel, or someone needs to do
some fiddly work in dma-direct to a) introduce the notion of an optional
global pool, and b) make it somehow cope with DMA_DIRECT_REMAP being
enabled but non-functional.
Thanks,
Robin.
