Messages in this thread | | | From | Guo Ren <> | Date | Mon, 7 Jun 2021 15:46:16 +0800 | Subject | Re: [PATCH RFC 0/3] riscv: Add DMA_COHERENT support |
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On Mon, Jun 7, 2021 at 2:51 PM Christoph Hellwig <hch@lst.de> wrote: > > On Mon, Jun 07, 2021 at 02:41:14PM +0800, Guo Ren wrote: > > Double/Triple the size of physical memory regions can't be accepted by > > SOC vendors, because it wastes HW resources. > > Some cost-down soc interconnects only have 32bit~34bit width of > > physical address, are you sure you could force them to expand it? (I > > can't) > > > > > or somewhat dynamic. > > How can HW implement with dynamic modifying PMA? What's the granularity? > > I'm just stating the requirements from the Linux DMA perspective. You > also do not need tripple the address space, just double.
With double, you only got "strong order + non-cache" for the DMA descriptor. How about write-combine scenario?
Even, double physical memory address space also wastes HW resources.
-- Best Regards Guo Ren
ML: https://lore.kernel.org/linux-csky/
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