linux-kernel - Re: [PATCH 3/8] mm: cma: Export a few symbols

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Date:   Mon, 20 Feb 2017 13:35:50 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Joonsoo Kim <js1304@...il.com>, m.szyprowski@...sung.com
Subject: Re: [PATCH 3/8] mm: cma: Export a few symbols

On Mon 13-02-17 14:44:16, Maxime Ripard wrote:
> Hi Michal,
> 
> On Thu, Feb 09, 2017 at 08:20:47PM +0100, Michal Hocko wrote:
> > [CC CMA people]
> > 
> > On Thu 09-02-17 17:39:17, Maxime Ripard wrote:
> > > Modules might want to check their CMA pool size and address for debugging
> > > and / or have additional checks.
> > > 
> > > The obvious way to do this would be through dev_get_cma_area and
> > > cma_get_base and cma_get_size, that are currently not exported, which
> > > results in a build failure.
> > > 
> > > Export them to prevent such a failure.
> > 
> > Who actually uses those exports. None of the follow up patches does
> > AFAICS.
> 
> This is for the ARM Mali GPU driver that is out of tree, unfortunately.

We do not export symbols which do not have any in-tree users.

> In one case (using the legacy fbdev API), the driver wants to (and
> probably should) validate that the buffer as indeed been allocated
> from the memory allocation pool.
> 
> Rob suggested that instead of hardcoding it to cover the whole RAM
> (which defeats the purpose of that check in the first place), we used
> the memory-region bindings in the DT and follow that, which does work
> great, but we still have to retrieve the base address and size of that
> region, hence why this patches are needed.

Anyway I would suggest talking to CMA people to find a better API for
modules to use...

-- 
Michal Hocko
SUSE Labs