Re: [PATCH v4 1/2] tty: hvc: pass DMA capable memory to put_chars()

On Thu, Aug 12, 2021 at 10:08 AM Xianting TIan
[off-list ref] wrote:

在 2021/8/6 下午10:51, Arnd Bergmann 写道:

quoted

On Fri, Aug 6, 2021 at 5:01 AM Xianting Tian

quoted

+#define __ALIGNED__ __attribute__((__aligned__(sizeof(long))))

I think you need a higher alignment for DMA buffers, instead of sizeof(long),
I would suggest ARCH_DMA_MINALIGN.

As some ARCH(eg, x86, riscv) doesn't define ARCH_DMA_MINALIG, so i think
it 's better remain the code unchanged,

I will send v5 patch soon.

I think you could just use "L1_CACHE_BYTES" as the alignment in this case.
This will make the structure slightly larger for architectures that do not have
alignment constraints on DMA buffers, but using a smaller alignment is
clearly wrong. Another option would be to use ARCH_KMALLOC_MINALIGN.

Note that there is a patch to add ARCH_DMA_MINALIGN to riscv already,
as some implementations do not have coherent DMA. I had failed to
realized though that on x86 you do not get an ARCH_DMA_MINALIGN
definition.

       Arnd