On 6/16/25 8:21 AM, Maxime Ripard wrote: > We've discussed a number of times of how some heap names are bad, but > not really what makes a good heap name. > > Let's document what we expect the heap names to look like. > > Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx> > Signed-off-by: Maxime Ripard <mripard@xxxxxxxxxx> > --- > Changes in v2: > - Added justifications for each requirement / suggestions > - Added a mention and example of buffer attributes > - Link to v1: https://lore.kernel.org/r/20250520-dma-buf-heap-names-doc-v1-1-ab31f74809ee@xxxxxxxxxx > --- > Documentation/userspace-api/dma-buf-heaps.rst | 38 +++++++++++++++++++++++++++ > 1 file changed, 38 insertions(+) > > diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst > index 535f49047ce6450796bf4380c989e109355efc05..835ad1c3a65bc07b6f41d387d85c57162909e859 100644 > --- a/Documentation/userspace-api/dma-buf-heaps.rst > +++ b/Documentation/userspace-api/dma-buf-heaps.rst > @@ -21,5 +21,43 @@ following heaps: > usually created either through the kernel commandline through the > `cma` parameter, a memory region Device-Tree node with the > `linux,cma-default` property set, or through the `CMA_SIZE_MBYTES` or > `CMA_SIZE_PERCENTAGE` Kconfig options. Depending on the platform, it > might be called ``reserved``, ``linux,cma``, or ``default-pool``. > + > +Naming Convention > +================= > + > +``dma-buf`` heaps name should meet a number of constraints: > + For these points below, I would s/That name/The name/ (3 places). > +- That name must be stable, and must not change from one version to the > + other. Userspace identifies heaps by their name, so if the names ever > + changes, we would be likely to introduce regressions. change, > + > +- That name must describe the memory region the heap will allocate from, > + and must uniquely identify it in a given platform. Since userspace > + applications use the heap name as the discriminant, it must be able to > + tell which heap it wants to use reliably if there's multiple heaps. if there are > + > +- That name must not mention implementation details, such as the > + allocator. The heap driver will change over time, and implementation > + details when it was introduced might not be relevant in the future. > + > +- The name should describe properties of the buffers that would be > + allocated. Doing so will make heap identification easier for > + userspace. Such properties are: > + > + - ``cacheable`` / ``uncacheable`` for buffers with CPU caches enabled > + or disabled; > + > + - ``contiguous`` for physically contiguous buffers; > + > + - ``protected`` for encrypted buffers not accessible the OS; > + > +- The name may describe intended usage. Doing so will make heap > + identification easier for userspace applications and users. > + > +For example, assuming a platform with a reserved memory region located > +at the RAM address 0x42000000, intended to allocate video framebuffers, > +physically contiguous, and backed by the CMA kernel allocator. Good ^^^ Not a complete sentence. Change '.' to ',': allocator, good > +names would be ``memory@42000000-cacheable-contiguous`` or > +``video@42000000``, but ``cma-video`` wouldn't. > > --- > base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494 > change-id: 20250520-dma-buf-heap-names-doc-31261aa0cfe6 > > Best regards, -- ~Randy
