Re: [PATCH 4/9] dma-buf: heaps: Add debugfs support

[John Stultz <jstultz@google.com>]

On Wed, Sep 3, 2025 at 8:38 AM Thierry Reding <thierry.reding@gmail.com> wrote:
>
> On Tue, Sep 02, 2025 at 03:37:45PM -0700, John Stultz wrote:
> > On Tue, Sep 2, 2025 at 8:46 AM Thierry Reding <thierry.reding@gmail.com> wrote:
> > >
> > > From: Thierry Reding <treding@nvidia.com>
> > >
> > > Add a callback to struct dma_heap_ops that heap providers can implement
> > > to show information about the state of the heap in debugfs. A top-level
> > > directory named "dma_heap" is created in debugfs and individual files
> > > will be named after the heaps.
> > >
> >
> > I know its debugfs, but this feels a little loosey-goosey as an uAPI.
>
> Well, the whole point of debugfs is that it's not really an ABI. Nothing
> should ever rely on the presence of these files.
>
> > Is there any expected format for the show function?
> >
> > What would other dmabuf heaps ideally export via this interface?
>
> I've thought about this a bit and I'm not sure it makes sense to
> standardize on this. I think on one hand having a list of buffers
> exported by the dma-buf heap is probably the lowest common denominator,
> but then there might be a bunch of other things that are very heap-
> specific that some heap might want to export.
>
> > Is there some consistent dma_heap-ish concept for it to justify it
> > being under a dma_heap directory, and not just an independent debugfs
> > file for the driver implementing the dmabuf heap?
>
> Well, I think just the fact that it's a dma-heap would qualify its
> corresponding debugfs to be in a well-known location. We could of course
> pick some arbitrary location, but that's just a recipe for chaos because
> then everybody puts these whereever they want. There's really no
> standard place for driver-specific debugfs files to go, so putting it
> into some "subsystem"-specific directory seems like the better option.

Ok, I guess I was thinking if the files are organizationally cohesive
to be under the dma-heap directory, they ought to have some
consistency between them.

But I can see your perspective here that organizing the driver
specific debug files in a directory helps with folks finding and
identifying it.

Thanks for clarifying!
-john