Re: [PATCH 2/2] drm/msm: Add MSM_WAIT_IOVA ioctl

[Brian Ho]

On Tue, Jan 14, 2020 at 08:48:48AM -0800, Rob Clark wrote:
> On Tue, Jan 14, 2020 at 8:40 AM Brian Ho <brian@xxxxxxxxx> wrote:
> >
> > On Mon, Jan 13, 2020 at 03:17:38PM -0800, Rob Clark wrote:
> > > On Mon, Jan 13, 2020 at 2:55 PM Brian Ho <brian@xxxxxxxxx> wrote:
> > > >
> > > > On Mon, Jan 13, 2020 at 09:57:43AM -0800, Kristian Kristensen wrote:
> > > > > On Mon, Jan 13, 2020 at 8:25 AM Rob Clark <robdclark@xxxxxxxxxxxx> wrote:
> > > > >
> > > > > > On Mon, Jan 13, 2020 at 7:37 AM Brian Ho <brian@xxxxxxxxx> wrote:
> > > > > > >
> > > > > > > Implements an ioctl to wait until a value at a given iova is greater
> > > > > > > than or equal to a supplied value.
> > > > > > >
> > > > > > > This will initially be used by turnip (open-source Vulkan driver for
> > > > > > > QC in mesa) for occlusion queries where the userspace driver can
> > > > > > > block on a query becoming available before continuing via
> > > > > > > vkGetQueryPoolResults.
> > > > > > >
> > > > > > > Signed-off-by: Brian Ho <brian@xxxxxxxxx>
> > > > > > > ---
> > > > > > >  drivers/gpu/drm/msm/msm_drv.c | 63 +++++++++++++++++++++++++++++++++--
> > > > > > >  include/uapi/drm/msm_drm.h    | 13 ++++++++
> > > > > > >  2 files changed, 74 insertions(+), 2 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/gpu/drm/msm/msm_drv.c
> > > > > > b/drivers/gpu/drm/msm/msm_drv.c
> > > > > > > index c84f0a8b3f2c..dcc46874a5a2 100644
> > > > > > > --- a/drivers/gpu/drm/msm/msm_drv.c
> > > > > > > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > > > > > > @@ -36,10 +36,11 @@
> > > > > > >   *           MSM_GEM_INFO ioctl.
> > > > > > >   * - 1.4.0 - softpin, MSM_RELOC_BO_DUMP, and GEM_INFO support to set/get
> > > > > > >   *           GEM object's debug name
> > > > > > > - * - 1.5.0 - Add SUBMITQUERY_QUERY ioctl
> > > > > > > + * - 1.5.0 - Add SUBMITQUEUE_QUERY ioctl
> > > > > > > + * - 1.6.0 - Add WAIT_IOVA ioctl
> > > > > > >   */
> > > > > > >  #define MSM_VERSION_MAJOR      1
> > > > > > > -#define MSM_VERSION_MINOR      5
> > > > > > > +#define MSM_VERSION_MINOR      6
> > > > > > >  #define MSM_VERSION_PATCHLEVEL 0
> > > > > > >
> > > > > > >  static const struct drm_mode_config_funcs mode_config_funcs = {
> > > > > > > @@ -952,6 +953,63 @@ static int msm_ioctl_submitqueue_close(struct
> > > > > > drm_device *dev, void *data,
> > > > > > >         return msm_submitqueue_remove(file->driver_priv, id);
> > > > > > >  }
> > > > > > >
> > > > > > > +static int msm_ioctl_wait_iova(struct drm_device *dev, void *data,
> > > > > > > +               struct drm_file *file)
> > > > > > > +{
> > > > > > > +       struct msm_drm_private *priv = dev->dev_private;
> > > > > > > +       struct drm_gem_object *obj;
> > > > > > > +       struct drm_msm_wait_iova *args = data;
> > > > > > > +       ktime_t timeout = to_ktime(args->timeout);
> > > > > > > +       unsigned long remaining_jiffies = timeout_to_jiffies(&timeout);
> > > > > > > +       struct msm_gpu *gpu = priv->gpu;
> > > > > > > +       void *base_vaddr;
> > > > > > > +       uint64_t *vaddr;
> > > > > > > +       int ret;
> > > > > > > +
> > > > > > > +       if (args->pad)
> > > > > > > +               return -EINVAL;
> > > > > > > +
> > > > > > > +       if (!gpu)
> > > > > > > +               return 0;
> > > > > >
> > > > > > hmm, I'm not sure we should return zero in this case.. maybe -ENODEV?
> > > > > >
> > > > > > > +
> > > > > > > +       obj = drm_gem_object_lookup(file, args->handle);
> > > > > > > +       if (!obj)
> > > > > > > +               return -ENOENT;
> > > > > > > +
> > > > > > > +       base_vaddr = msm_gem_get_vaddr(obj);
> > > > > > > +       if (IS_ERR(base_vaddr)) {
> > > > > > > +               ret = PTR_ERR(base_vaddr);
> > > > > > > +               goto err_put_gem_object;
> > > > > > > +       }
> > > > > > > +       if (args->offset + sizeof(*vaddr) > obj->size) {
> > > > > > > +               ret = -EINVAL;
> > > > > > > +               goto err_put_vaddr;
> > > > > > > +       }
> > > > > > > +
> > > > > > > +       vaddr = base_vaddr + args->offset;
> > > > > > > +
> > > > > > > +       /* Assumes WC mapping */
> > > > > > > +       ret = wait_event_interruptible_timeout(
> > > > > > > +                       gpu->event, *vaddr >= args->value,
> > > > > > remaining_jiffies);
> > > > > >
> > > > >
> > > > > This needs to do the awkward looking
> > > > >
> > > > >   (int64_t)(*data - value) >= 0
> > > > >
> > > > > to properly handle the wraparound case.
> > > > >
> > > >
> > > > I think this comparison will run into issues if we allow for 64-bit
> > > > reference values. For example, if value is ULLONG_MAX, and *data
> > > > starts at 0 on the first comparison, we'll immediately return.
> > > >
> > > > It's not too much of an issue in fence_completed (msm_fence.c), but
> > > > in this ioctl, *data can grow at an arbitrary rate. Are we concerned
> > > > about this?
> > > >
> > > > > > +
> > > > > > > +       if (ret == 0) {
> > > > > > > +               ret = -ETIMEDOUT;
> > > > > > > +               goto err_put_vaddr;
> > > > > > > +       } else if (ret == -ERESTARTSYS) {
> > > > > > > +               goto err_put_vaddr;
> > > > > > > +       }
> > > > > >
> > > > > > maybe:
> > > > > >
> > > > > >  } else {
> > > > > >    ret = 0;
> > > > > >  }
> > > > > >
> > > > > > and then drop the next three lines?
> > > > > >
> > > > > > > +
> > > > > > > +       msm_gem_put_vaddr(obj);
> > > > > > > +       drm_gem_object_put_unlocked(obj);
> > > > > > > +       return 0;
> > > > > > > +
> > > > > > > +err_put_vaddr:
> > > > > > > +       msm_gem_put_vaddr(obj);
> > > > > > > +err_put_gem_object:
> > > > > > > +       drm_gem_object_put_unlocked(obj);
> > > > > > > +       return ret;
> > > > > > > +}
> > > > > > > +
> > > > > > >  static const struct drm_ioctl_desc msm_ioctls[] = {
> > > > > > >         DRM_IOCTL_DEF_DRV(MSM_GET_PARAM,    msm_ioctl_get_param,
> > > > > > DRM_RENDER_ALLOW),
> > > > > > >         DRM_IOCTL_DEF_DRV(MSM_GEM_NEW,      msm_ioctl_gem_new,
> > > > > > DRM_RENDER_ALLOW),
> > > > > > > @@ -964,6 +1022,7 @@ static const struct drm_ioctl_desc msm_ioctls[] = {
> > > > > > >         DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_NEW,
> > > > > >  msm_ioctl_submitqueue_new,   DRM_RENDER_ALLOW),
> > > > > > >         DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_CLOSE,
> > > > > > msm_ioctl_submitqueue_close, DRM_RENDER_ALLOW),
> > > > > > >         DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_QUERY,
> > > > > > msm_ioctl_submitqueue_query, DRM_RENDER_ALLOW),
> > > > > > > +       DRM_IOCTL_DEF_DRV(MSM_WAIT_IOVA, msm_ioctl_wait_iova,
> > > > > > DRM_RENDER_ALLOW),
> > > > > > >  };
> > > > > > >
> > > > > > >  static const struct vm_operations_struct vm_ops = {
> > > > > > > diff --git a/include/uapi/drm/msm_drm.h b/include/uapi/drm/msm_drm.h
> > > > > > > index 0b85ed6a3710..8477f28a4ee1 100644
> > > > > > > --- a/include/uapi/drm/msm_drm.h
> > > > > > > +++ b/include/uapi/drm/msm_drm.h
> > > > > > > @@ -298,6 +298,17 @@ struct drm_msm_submitqueue_query {
> > > > > > >         __u32 pad;
> > > > > > >  };
> > > > > > >
> > > > > > > +/* This ioctl blocks until the u64 value at bo + offset is greater than
> > > > > > or
> > > > > > > + * equal to the reference value.
> > > > > > > + */
> > > > > > > +struct drm_msm_wait_iova {
> > > > > > > +       __u32 handle;          /* in, GEM handle */
> > > > > > > +       __u32 pad;
> > > > > > > +       struct drm_msm_timespec timeout;   /* in */
> > > > > > > +       __u64 offset;          /* offset into bo */
> > > > > > > +       __u64 value;           /* reference value */
> > > > > >
> > > > > > Maybe we should go ahead and add a __u64 mask;
> > > > > >
> > > > > > that would let us wait for 32b values as well, and wait for bits in a
> > > > > > bitmask
> > > > > >
> > > > >
> > > > > I think we'd be OK to just default to 32 bit values instead, since most of
> > > > > the CP commands that this is intended to work with (CP_EVENT_WRITE,
> > > > > CP_WAIT_MEM_GTE etc) operate on 32 bit values. We could move 'value' to the
> > > > > slot right after 'handle' but then we'd not have any pad/reserved fields.
> > > > > Maybe we keep 'value' 64 bit but restrict it to 32 bits, with an option to
> > > > > add a 64 bit flag in 'pad' later on?
> > > > >
> > > >
> > > > FWIW, the current usage of this in my mesa MR uses a 64 bit value.
> > > > There's no super great reason that the available bit is 64 bits and
> > > > not 32 bits (I think it made the addressing math a bit simpler), but
> > > > I'm fine with whatever you all decide on here.
> > > >
> > >
> > > I assume you are waiting for a fence value written w/ CP_EVENT_WRITE?
> > > Or at least that is what I'd recommend.  That would be 32b
> > >
> > > BR,
> > > -R
> > >
> >
> > So it's actually a little bit different than that. I allocate a bo
> > for the occlusion query which has an "availability" bit (0 for
> > unavailable, 1 for available). When the occlusion query ends, we
> > write the fragments passed value to the bo via CP_EVENT_WRITE and
> > then wait for that write to complete before setting the available
> > bit to 1 via a simple CP_MEM_WRITE [1].
> >
> > It's that CP_MEM_WRITE that I plan on waiting on with this new iova
> > ioctl.
> >
> > [1] https://gitlab.freedesktop.org/mesa/mesa/blob/768106c50a5569796bb6d5e04b5e4d65c1d00ea0/src/freedreno/vulkan/tu_query.c#L529
> >
> 
> hmm, interesting.. I had in mind something more like:
> 
> https://gitlab.freedesktop.org/drm/msm/blob/msm-next/drivers/gpu/drm/msm/adreno/a6xx_gpu.c#L137
> 
> The high bit in the first dword of the packet (which we probably
> shouldn't open-code) is the "give me an irq after the value in last
> dword is written to memory"..
> 
> (I haven't checked yet whether we can use the "gimme an irq" bit from userspace)
> 
> BR,
> -R

I see. Let's continue discussing this on the mesa MR because there's
more context there.

Regardless of how we end up implementing vkCmdEndQuery, I think it
will be safe to default to 32 bit values for this ioctl and have a
flag to use 64 bit instead like Kristian suggested. If that sounds
good to you, I'll go ahead and make the change for the v2 patch
series.