Re: [PATCH 1/2] drm: add cache support for arm64

[Rob Clark]

On Tue, Aug 6, 2019 at 9:23 AM Rob Clark <robdclark@xxxxxxxxxxxx> wrote:
>
> On Tue, Aug 6, 2019 at 8:50 AM Christoph Hellwig <hch@xxxxxx> wrote:
> >
> > On Tue, Aug 06, 2019 at 07:11:41AM -0700, Rob Clark wrote:
> > > Agreed that drm_cflush_* isn't a great API.  In this particular case
> > > (IIUC), I need wb+inv so that there aren't dirty cache lines that drop
> > > out to memory later, and so that I don't get a cache hit on
> > > uncached/wc mmap'ing.
> >
> > So what is the use case here?  Allocate pages using the page allocator
> > (or CMA for that matter), and then mmaping them to userspace and never
> > touching them again from the kernel?
>
> Currently, it is pages coming from tmpfs.  Ideally we want pages that
> are swappable when unpinned.

to be more specific, pages come from
shmem_file_setup()/shmem_read_mapping_page()

BR,
-R