Re: [PATCH v2 2/2] riscv: enable DMA_BOUNCE_UNALIGNED_KMALLOC for !dma_coherent

[Conor Dooley]

On Mon, Jul 17, 2023 at 12:51:47AM +0800, Jisheng Zhang wrote:
> With the DMA bouncing of unaligned kmalloc() buffers now in place,
> enable it for riscv when RISCV_DMA_NONCOHERENT=y to allow the
> kmalloc-{8,16,32,96} caches. Since RV32 doesn't enable SWIOTLB
> yet, and I didn't see any dma noncoherent RV32 platforms in the
> mainline, so skip RV32 now by only enabling
> DMA_BOUNCE_UNALIGNED_KMALLOC if SWIOTLB is available. Once we see
> such requirement on RV32, we can enable it then.
> 
> NOTE: we didn't force to create the swiotlb buffer even when the
> end of RAM is within the 32-bit physical address range. That's to
> say:
> For RV64 with > 4GB memory, the feature is enabled.
> For RV64 with <= 4GB memory, the feature isn't enabled by default. We
> rely on users to pass "swiotlb=mmnn,force" where mmnn is the Number of
> I/O TLB slabs, see kernel-parameters.txt for details.
> 
> Tested on Sipeed Lichee Pi 4A with 8GB DDR and Sipeed M1S BL808 Dock
> board.
> 
> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>

Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>

Thanks,
Conor.

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