Re: [PATCH 1/2] gpu: host1x: Allow entries in BO caches to be freed

[Thierry Reding]

On Fri, May 15, 2026 at 11:34:51AM +0900, Mikko Perttunen wrote:
> When a buffer object is pinned via host1x_bo_pin() with a cache, the
> resulting mapping is kept in the cache so it can be reused on subsequent
> pins. Each mapping held a reference to the underlying host1x_bo (taken
> in tegra_bo_pin / gather_bo_pin), so as long as a mapping was cached,
> the bo itself could not be freed.
> 
> However, the only way to remove the cached mapping was through the free
> path of the buffer object. This meant that if a bo got cached, it could
> never get freed again.
> 
> Resolve the circularity by holding a weak reference to the bo from the
> cache side. This is done by having the .pin callbacks not bump the bo's
> refcount -- instead the common Host1x bo code does so, except for the
> cache reference.
> 
> Also move the remove-cache-mapping-on-free code into a common function
> inside Host1x code. This is only called from the TegraDRM GEM buffers
> since those are the only ones that can be cached at the moment.
> 
> Reported-by: Aaron Kling <webgeek1234@xxxxxxxxx>
> Fixes: 1f39b1dfa53c ("drm/tegra: Implement buffer object cache")
> Signed-off-by: Mikko Perttunen <mperttunen@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/tegra/gem.c    | 13 ++-------
>  drivers/gpu/drm/tegra/submit.c |  3 +--
>  drivers/gpu/host1x/bus.c       | 60 +++++++++++++++++++++++++++++++++++++++++-
>  include/linux/host1x.h         |  7 +++++
>  4 files changed, 69 insertions(+), 14 deletions(-)

Applied, thanks.

Thierry

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