Re: [PATCH 1/2] MIPS: Define pgprot_dmacoherent according to coherentio status

[Christoph Hellwig]

On Mon, Jan 13, 2020 at 11:11:58PM +0800, Jiaxun Yang wrote:
> 
> 
> ä 2020å1æ13æ GMT+08:00 äå10:58:20, Christoph Hellwig <hch@xxxxxx> åå:
> >On Mon, Jan 13, 2020 at 10:07:04PM +0800, Jiaxun Yang wrote:
> >> For MIPS chips that support coherentio DMA, it's always safe
> >> to make DMA requests cached.
> >
> >For DMA coherent devices pgprot_dmacoherent isn't even used, so this
> >doesn't make sense.
> 
> Hi,
> 
> I'm supposed to use it later in drm/ttm
>  ttm_bo_util to overwrite pgprot for TTM_PL_SYSTEM.
> And I wish this pgropt can always represent dmacoherent pgropt.
> Would it be fine?

No code outside the core DMA code has any business using
pgprot_dmacoherent.