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

From: Brian Ho
Date: Tue Jan 14 2020 - 11:40:55 EST

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

> > > >
> > > > Other than those minor comments, it looks pretty good to me
> > > >
> > > > BR,
> > > > -R
> > > >
> > > > > +};
> > > > > +
> > > > > #define DRM_MSM_GET_PARAM 0x00
> > > > > /* placeholder:
> > > > > #define DRM_MSM_SET_PARAM 0x01
> > > > > @@ -315,6 +326,7 @@ struct drm_msm_submitqueue_query {
> > > > > #define DRM_MSM_SUBMITQUEUE_NEW 0x0A
> > > > > #define DRM_MSM_SUBMITQUEUE_CLOSE 0x0B
> > > > > #define DRM_MSM_SUBMITQUEUE_QUERY 0x0C
> > > > > +#define DRM_MSM_WAIT_IOVA 0x0D
> > > > >
> > > > > #define DRM_IOCTL_MSM_GET_PARAM DRM_IOWR(DRM_COMMAND_BASE +
> > > > DRM_MSM_GET_PARAM, struct drm_msm_param)
> > > > > #define DRM_IOCTL_MSM_GEM_NEW DRM_IOWR(DRM_COMMAND_BASE +
> > > > DRM_MSM_GEM_NEW, struct drm_msm_gem_new)
> > > > > @@ -327,6 +339,7 @@ struct drm_msm_submitqueue_query {
> > > > > #define DRM_IOCTL_MSM_SUBMITQUEUE_NEW DRM_IOWR(DRM_COMMAND_BASE +
> > > > DRM_MSM_SUBMITQUEUE_NEW, struct drm_msm_submitqueue)
> > > > > #define DRM_IOCTL_MSM_SUBMITQUEUE_CLOSE DRM_IOW (DRM_COMMAND_BASE +
> > > > DRM_MSM_SUBMITQUEUE_CLOSE, __u32)
> > > > > #define DRM_IOCTL_MSM_SUBMITQUEUE_QUERY DRM_IOW (DRM_COMMAND_BASE +
> > > > DRM_MSM_SUBMITQUEUE_QUERY, struct drm_msm_submitqueue_query)
> > > > > +#define DRM_IOCTL_MSM_WAIT_IOVA DRM_IOW (DRM_COMMAND_BASE +
> > > > DRM_MSM_WAIT_IOVA, struct drm_msm_wait_iova)
> > > > >
> > > > > #if defined(__cplusplus)
> > > > > }
> > > > > --
> > > > > 2.25.0.rc1.283.g88dfdc4193-goog
> > > > >
> > > >