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 <ad97096f-cc90-4f20-0f73-f33e9b275f1a@collabora.com>
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From:   Rob Clark <robdclark@gmail.com>
Date:   Thu, 31 Mar 2022 12:02:35 -0700
Message-ID: <CAF6AEGvZqM1OT_n1C+x+C1GTd4PbFkH4c7P-BseDOUGj7yj3Eg@mail.gmail.com>
Subject: Re: [PATCH v2 10/10] drm/msm: Add a way for userspace to allocate GPU iova
To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>,
        freedreno <freedreno@lists.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Rob Clark <robdclark@chromium.org>,
        Sean Paul <sean@poorly.run>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Akhil P Oommen <quic_akhilpo@quicinc.com>,
        Jonathan Marek <jonathan@marek.ca>,
        Jordan Crouse <jordan@cosmicpenguin.net>,
        Emma Anholt <emma@anholt.net>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        open list <linux-kernel@vger.kernel.org>
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On Thu, Mar 31, 2022 at 11:52 AM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> ...
> > +/*
> > + * Get the requested iova but don't pin it.  Fails if the requested iova is
> > + * not available.  Doesn't need a put because iovas are currently valid for
> > + * the life of the object.
> > + *
> > + * Setting an iova of zero will clear the vma.
> > + */
> > +int msm_gem_set_iova(struct drm_gem_object *obj,
> > +                  struct msm_gem_address_space *aspace, uint64_t iova)
> > +{
> > +     int ret = 0;
>
> nit: No need to initialize the ret

actually, we do

> > +     msm_gem_lock(obj);
> > +     if (!iova) {
> > +             ret = clear_iova(obj, aspace);
> > +     } else {
> > +             struct msm_gem_vma *vma;
> > +             vma = get_vma_locked(obj, aspace, iova, iova + obj->size);
> > +             if (IS_ERR(vma)) {
> > +                     ret = PTR_ERR(vma);
> > +             } else if (GEM_WARN_ON(vma->iova != iova)) {
> > +                     clear_iova(obj, aspace);
> > +                     ret = -ENOSPC;
>
> The (vma->iova != iova) means that vma is already set, but to a
> different address. Is -ENOSPC really appropriate here? -EBUSY or -EINVAL
> looks more natural to me.

yeah, -EBUSY is better

> > +             }
> > +     }
> > +     msm_gem_unlock(obj);
> > +
> > +     return ret;
> > +}
> > +
> >  /*
> >   * Unpin a iova by updating the reference counts. The memory isn't actually
> >   * purged until something else (shrinker, mm_notifier, destroy, etc) decides
> > diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
> > index 38d66e1248b1..efa2e5c19f1e 100644
> > --- a/drivers/gpu/drm/msm/msm_gem.h
> > +++ b/drivers/gpu/drm/msm/msm_gem.h
> > @@ -38,6 +38,12 @@ struct msm_gem_address_space {
> >
> >       /* @faults: the number of GPU hangs associated with this address space */
> >       int faults;
> > +
> > +     /** @va_start: lowest possible address to allocate */
> > +     uint64_t va_start;
> > +
> > +     /** @va_size: the size of the address space (in bytes) */
> > +     uint64_t va_size;
> >  };
> >
> >  struct msm_gem_address_space *
> > @@ -144,6 +150,8 @@ struct msm_gem_vma *msm_gem_get_vma_locked(struct drm_gem_object *obj,
> >                                          struct msm_gem_address_space *aspace);
> >  int msm_gem_get_iova(struct drm_gem_object *obj,
> >               struct msm_gem_address_space *aspace, uint64_t *iova);
> > +int msm_gem_set_iova(struct drm_gem_object *obj,
> > +             struct msm_gem_address_space *aspace, uint64_t iova);
> >  int msm_gem_get_and_pin_iova_range(struct drm_gem_object *obj,
> >               struct msm_gem_address_space *aspace, uint64_t *iova,
> >               u64 range_start, u64 range_end);
> nit: There is an odd mix of uint64_t and u64 (and alike) in the MSM code
> :) The uint64_t variant shouldn't be used by kernel code in general and
> checkpatch should want about it.

one of many things that I disagree with checkpatch about ;-)

I prefer standard types to custom ones.  I _kinda_ get the argument in
case of uapi (but IMHO that doesn't apply to how drm uapi headers are
used)

BR,
-R