[PATCH v2] Documentation: dma-buf: heaps: Add heap name definitions

[Maxime Ripard]

Hi,

On Thu, Dec 05, 2024 at 03:17:57PM -0800, John Stultz wrote:
> On Tue, Dec 3, 2024 at 11:04 AM Andrew Davis <afd at ti.com> wrote:
> > On 12/3/24 1:44 AM, Maxime Ripard wrote:
> > > On Mon, Dec 02, 2024 at 11:12:23AM -0800, John Stultz wrote:
> > >> Hrm. I'm not sure I see the value in enumerating things in this way,
> > >> it seems like it will be a nuisance to keep current?  Maybe something
> > >> like:
> > >>
> > >> On most systems the default cma region is named "linux, cma" or
> > >> "reserved", with a few exceptions:
> > >>      - Allwinner sun4i, sun5i and sun7i families: ``default-pool``
> > >
> > > I'm a bit worried about doing so. What if, on a "linux,cma" system, we
> > > have another "reserved" heap created with different semantics?
> > >
> >
> > Having the "default CMA" heap get its dev name based on the method that
> > created it was arguably a mistake made when first upstreaming this heap.
> > We should fix this, then maybe add the old name as a link just for
> > backwards compat as needed.
> >
> > exp_info.name = "default_cma";
> >
> > All other CMA and carveout heaps will have names based on their
> > method of creation as there may be multiple of them, but there
> > will only every be one "default CMA" area, and its heap should
> > be named to match.
> 
> This seems reasonable to me. Maybe putting the link creation behind a
> compatibility config so they can be later deprecated?

I gave it a look, and while I'm not super experienced with fs in
general, it looks like there's no easy way to create a symbolic link
in devtmpfs from the kernel.

I also tried to cheat a little and create another device file with the
same major/minor, but that doesn't look trivial to me either.

Do you know how to do so, or are aware of any other part of the kernel
doing something similar?

Most importantly, do you consider it a requirement before merging that
patch?

Maxime
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