On Tue, Sep 6, 2022 at 8:59 PM Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > > On Tue, Sep 06, 2022 at 03:34:02PM +0300, Oded Gabbay wrote: > > > > > > > + /* > > > > > > + * Since the memory being mapped is a device memory it could never be in > > > > > > + * CPU caches. > > > > > > + */ > > > > > DMA_ATTR_SKIP_CPU_SYNC doesn't even apply to dma_map_resource, not sure > > > > > where this wisdom comes from. > > > > > > Habana driver > > I hate to throw the ball at someone else, but I actually copied the > > code from the amdgpu driver, from amdgpu_vram_mgr_alloc_sgt() iirc. > > And if you remember Jason, you asked why we use this specific define > > in the original review you did and I replied the following (to which > > you agreed and that's why we added the comment): > > Yes, I remember, but Christophs remark is that DMA_ATTR_SKIP_CPU_SYNC > doesn't even do anything when passed to dma_map_resource(). > > The only attr that seems to be used is DMA_ATTR_PRIVILEGED from what I > can see. > > Jason Yes, it appears he is correct. Probably what happened is that either this was originally copied from a use of dma_map_page or something similar that does check this attribute, or maybe dma_map_resource used it in the past and the underlying code has changed. Regardless, it seems we can remove it from the calls to dma_map_resource. I went over the kernel code and it seems only habana and amdgpu (and amdkfd) are passing this property to dma_map_resource. All other callers just pass 0. Oded
