Re: [PATCH 2/2] drm/tegra: Acquire a reference to the IOVA cache

[Thierry Reding <thierry.reding@gmail.com>]

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On Thu, May 17, 2018 at 01:53:23PM +0300, Dmitry Osipenko wrote:
> On 23.04.2018 09:57, Thierry Reding wrote:
> > From: Thierry Reding <treding@nvidia.com>
> > 
> > The IOVA API uses a memory cache to allocate IOVA nodes from. To make
> > sure that this cache is available, obtain a reference to it and release
> > the reference when the cache is no longer needed.
> > 
> > On 64-bit ARM this is hidden by the fact that the DMA mapping API gets
> > that reference and never releases it. On 32-bit ARM, however, the DMA
> > mapping API doesn't do that, so allocation of IOVA nodes fails.
> > 
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> >  drivers/gpu/drm/tegra/drm.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
> > index 4a696fa274a3..0540b0741df6 100644
> > --- a/drivers/gpu/drm/tegra/drm.c
> > +++ b/drivers/gpu/drm/tegra/drm.c
> > @@ -115,6 +115,10 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
> >  			goto free;
> >  		}
> >  
> > +		err = iova_cache_get();
> > +		if (err < 0)
> > +			goto domain;
> > +
> >  		geometry = &tegra->domain->geometry;
> >  		gem_start = geometry->aperture_start;
> >  		gem_end = geometry->aperture_end - CARVEOUT_SZ;
> > @@ -205,11 +209,12 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
> >  	tegra_drm_fb_free(drm);
> >  config:
> >  	drm_mode_config_cleanup(drm);
> > -
> > +domain:
> >  	if (tegra->domain) {
> >  		mutex_destroy(&tegra->mm_lock);
> >  		drm_mm_takedown(&tegra->mm);
> >  		put_iova_domain(&tegra->carveout.domain);
> > +		iova_cache_put();
> 
> I've spotted that this ^ is incorrect. This will put the iova_cache without
> getting it if iova_cache_get() failed.

Good catch, updated the patch with your suggestion.

Thanks,
Thierry

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