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

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Date:   Tue, 6 Aug 2019 09:26:16 -0700
From:   Rob Clark <robdclark@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Rob Clark <robdclark@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm: add cache support for arm64

On Tue, Aug 6, 2019 at 9:23 AM Rob Clark <robdclark@...omium.org> wrote:
>
> On Tue, Aug 6, 2019 at 8:50 AM Christoph Hellwig <hch@....de> 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