On Mon, Jan 13, 2020 at 11:11:58PM +0800, Jiaxun Yang wrote:

于 2020年1月13日 GMT+08:00 下午10:58:20, Christoph Hellwig [off-list ref] 写到:

quoted

On Mon, Jan 13, 2020 at 10:07:04PM +0800, Jiaxun Yang wrote:

quoted

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.