[AMD Official Use Only - General]
> -----Original Message-----
> From: Imre Deak <imre.d...@intel.com>
> Sent: Friday, August 25, 2023 9:56 PM
> To: Lin, Wayne <wayne....@amd.com>
> Cc: dri-de...@lists.freedesktop.org; amd-gfx@lists.freedesktop.org;
> ly...@redhat.com; jani.nik...@intel.com; ville.syrj...@linux.intel.com;
> Wentland, Harry <harry.wentl...@amd.com>; Zuo, Jerry
> <jerry....@amd.com>
> Subject: Re: [PATCH 3/3] drm/mst: adjust the function
> drm_dp_remove_payload_part2()
>
> On Wed, Aug 23, 2023 at 03:16:44AM +0000, Lin, Wayne wrote:
> > [AMD Official Use Only - General]
> >
> > > -----Original Message-----
> > > From: Imre Deak <imre.d...@intel.com>
> > > Sent: Saturday, August 19, 2023 1:46 AM
> > > To: Lin, Wayne <wayne....@amd.com>
> > > Cc: dri-de...@lists.freedesktop.org; amd-gfx@lists.freedesktop.org;
> > > ly...@redhat.com; jani.nik...@intel.com;
> > > ville.syrj...@linux.intel.com; Wentland, Harry
> > > <harry.wentl...@amd.com>; Zuo, Jerry <jerry....@amd.com>
> > > Subject: Re: [PATCH 3/3] drm/mst: adjust the function
> > > drm_dp_remove_payload_part2()
> > >
> > > On Tue, Aug 08, 2023 at 03:47:47AM +0000, Lin, Wayne wrote:
> > > > [AMD Official Use Only - General]
> > > >
> > > > > -----Original Message-----
> > > > > From: Imre Deak <imre.d...@intel.com>
> > > > > Sent: Tuesday, August 8, 2023 12:00 AM
> > > > > To: Lin, Wayne <wayne....@amd.com>
> > > > > Cc: dri-de...@lists.freedesktop.org;
> > > > > amd-gfx@lists.freedesktop.org; ly...@redhat.com;
> > > > > jani.nik...@intel.com; ville.syrj...@linux.intel.com; Wentland,
> > > > > Harry <harry.wentl...@amd.com>; Zuo, Jerry <jerry....@amd.com>
> > > > > Subject: Re: [PATCH 3/3] drm/mst: adjust the function
> > > > > drm_dp_remove_payload_part2()
> > > > >
> > > > > On Mon, Aug 07, 2023 at 02:43:02AM +0000, Lin, Wayne wrote:
> > > > > > [AMD Official Use Only - General]
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Imre Deak <imre.d...@intel.com>
> > > > > > > Sent: Friday, August 4, 2023 11:32 PM
> > > > > > > To: Lin, Wayne <wayne....@amd.com>
> > > > > > > Cc: dri-de...@lists.freedesktop.org;
> > > > > > > amd-gfx@lists.freedesktop.org; ly...@redhat.com;
> > > > > > > jani.nik...@intel.com; ville.syrj...@linux.intel.com;
> > > > > > > Wentland, Harry <harry.wentl...@amd.com>; Zuo, Jerry
> > > > > > > <jerry....@amd.com>
> > > > > > > Subject: Re: [PATCH 3/3] drm/mst: adjust the function
> > > > > > > drm_dp_remove_payload_part2()
> > > > > > >
> > > > > > > On Fri, Aug 04, 2023 at 02:20:29PM +0800, Wayne Lin wrote:
> > > > > > > > [...]
> > > > > > > > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > > > > > > b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > > > > > > index e04f87ff755a..4270178f95f6 100644
> > > > > > > > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > > > > > > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > > > > > > @@ -3382,8 +3382,7 @@
> > > > > > > EXPORT_SYMBOL(drm_dp_remove_payload_part1);
> > > > > > > > * drm_dp_remove_payload_part2() - Remove an MST payload
> > > locally
> > > > > > > > * @mgr: Manager to use.
> > > > > > > > * @mst_state: The MST atomic state
> > > > > > > > - * @old_payload: The payload with its old state
> > > > > > > > - * @new_payload: The payload with its latest state
> > > > > > > > + * @payload: The payload with its latest state
> > > > > > > > *
> > > > > > > > * Updates the starting time slots of all other payloads
> > > > > > > > which would have
> > > > > > > been shifted towards
> > > > > > > > * the start of the payload ID table as a result of
> > > > > > > > removing a payload. Driver should call this @@ -3392,25
> > > > > > > > +3391,36 @@
> > > > > > > EXPORT_SYMBOL(drm_dp_remove_payload_part1);
> > > > > > > > */
> > > > > > > > void drm_dp_remove_payload_part2(struct
> > > > > drm_dp_mst_topology_mgr
> > > > > > > *mgr,
> > > > > > > > struct
> > > > > > > > drm_dp_mst_topology_state
> > > > > > > *mst_state,
> > > > > > > > - const struct
> > > > > > > > drm_dp_mst_atomic_payload
> > > > > > > *old_payload,
> > > > > > > > - struct drm_dp_mst_atomic_payload
> > > > > > > *new_payload)
> > > > > > > > + struct
> > > > > > > > + drm_dp_mst_atomic_payload
> > > > > > > *payload)
> > > > > > > > {
> > > > > > > > struct drm_dp_mst_atomic_payload *pos;
> > > > > > > > + u8 time_slots_to_remove;
> > > > > > > > + u8 next_payload_vc_start = mgr->next_start_slot;
> > > > > > > > +
> > > > > > > > + /* Find the current allocated time slot number of the
> > > > > > > > payload */
> > > > > > > > + list_for_each_entry(pos, &mst_state->payloads, next) {
> > > > > > > > + if (pos != payload &&
> > > > > > > > + pos->vc_start_slot > payload->vc_start_slot &&
> > > > > > > > + pos->vc_start_slot < next_payload_vc_start)
> > > > > > > > + next_payload_vc_start = pos->vc_start_slot;
> > > > > > > > + }
> > > > > > > > +
> > > > > > > > + time_slots_to_remove = next_payload_vc_start -
> > > > > > > > +payload->vc_start_slot;
> > > > > > >
> > > > > > > Imo, the intuitive way would be to pass the old payload
> > > > > > > state to this function - which already contains the required
> > > > > > > time_slots param
> > > > > > > - and refactor things instead moving vc_start_slot from the
> > > > > > > payload state to mgr suggested by Ville earlier.
> > > > > > >
> > > > > > > --Imre
> > > > > >
> > > > > > Hi Imre,
> > > > > > Thanks for your feedback!
> > > > > >
> > > > > > I understand it's functionally correct. But IMHO, it's still a
> > > > > > bit conceptually different between the time slot in old state
> > > > > > and the time slot in current payload table. My thought is the
> > > > > > time slot at the moment when we are removing the payload would
> > > > > > be a better
> > > choice.
> > > > >
> > > > > Yes, they are different. The old state contains the time slot
> > > > > the payload was added with in a preceding commit and so the time
> > > > > slot value which should be used when removing the same payload
> > > > > in the
> > > current commit.
> > > > >
> > > > > The new state contains a time slot value with which the payload
> > > > > will be added in the current commit and can be different than
> > > > > the one in the old state if the current commit has changed the
> > > > > payload size (meaning that the same atomic commit will first
> > > > > remove the payload using the time slot value in the old state
> > > > > and afterwards will add back the same payload using the time slot
> > > > > value
> in the new state).
> > > > >
> > > > Appreciate your time, Imre!
> > > >
> > > > Yes I understand, so I'm not using the number of the time slot in
> > > > the new
> > > state.
> > > > I'm referring to the start slot instead which is updated during
> > > > every allocation and removement at current commit.
> > > >
> > > > Like what you said, current commit manipulation could be a mix of
> > > > allocations and removements for the payload. My thought is,
> > > > conceptually, looking up the latest number of time slot is a
> > > > better choice
> > > rather than the one in old state.
> > > > It's relatively intuitive to me since we are removing payload from
> > > > current payload table and which changes since last preceding
> > > > commit till the moment we're deleting the payload. Although it's
> > > > unreasonable that these values are different.
> > > >
> > > > > > And with this, we can also simplify some codes. Especially
> > > > > > remove workaround in amd driver. In fact, DRM mst code
> > > > > > maintains the payload table and all the time slot info is in
> > > > > > it already. We don't really have to pass a new parameter.
> > > > >
> > > > > I agree that drm_dp_remove_payload() could be simplified, but
> > > > > this should be done so that the drivers can pass the old payload
> > > > > state to it (without having to pass the new state). This would
> > > > > be possible if vc_start_slot was not tracked in the payload
> > > > > state (which is really not an atomic state that can be
> > > > > precomputed as all other atomic state), rather it would be tracked in
> struct drm_dp_mst_topology_mgr.
> > > > >
> > > >
> > > > So the reason I chose to pass the new state is like what I
> > > > mentioned above. I would prefer to carry the latest updated
> > > > payload table instead which is in the new state. And I agree with
> > > > the explanation for the vc_start_slot and that's also my thought
> > > > at the beginning. It could be a refactor later, but no matter the
> > > > start slot is put into payload state or the topology manager I
> > > > would prefer to refer to the latest
> > > payload table rather than the number of time slot in the old state.
> > > >
> > > > > It looks like AMD has to reconstruct the old state in
> > > > > dm_helpers_construct_old_payload(). Could you explain why it
> > > > > couldn't instead just pass old_payload acquired by
> > > > >
> > > > > old_mst_state = drm_atomic_get_old_mst_topology_state();
> > > > > old_payload = drm_atomic_get_mst_payload_state(old_mst_state);
> > > > >
> > > > > ?
> > > >
> > > > AMD doesn't pass the drm old state to the stage while HW is
> > > > deleting the payload. The reason is that HW payload table is
> > > > known during HW programming procedure, so the payload removement
> > > > is based on the table at the moment.
> > > >
> > > > AMD expected the current number of time slot is also already
> > > > maintained in drm layer.
> > >
> > > Yes, both of the above are maintained by the drm layer, but it also
> > > means it doesn't really need to recalculate time_slots_to_remove as
> > > done in this patch, since that info is already available in the old
> > > payload
> state.
> > >
> > > Afaics the AMD driver calls properly
> > >
> > > drm_atomic_helper_commit() -> drm_atomic_helper_swap_state()
> > >
> > > after a commit, so that all the payloads it added should be tracked
> > > now as the old payload state.
> > >
> > > So could you confirm what is the old_payload->time_slots value
> > > (which you get with the above functions) at the point of removing
> > > this payload and if it's not the time_slots value this same payload
> > > was actually added with previously, why this is so (via some example
> sequence)?
> > >
> > > Thanks.
> >
> > Hi Imre,
> > I'm not saying that the time_slots carried in the old state is wrong within
> amd driver.
> > But just amd driver doesn't carry the drm state to the step when it's
> > removing the payload, since the info is already in its hardware and
> > drm used to maintain the info in the drm layer.
>
> Hm, in
>
> dm_helpers_dp_mst_write_payload_allocation_table()
>
> the
>
> mst_state = to_drm_dp_mst_topology_state(mst_mgr->base.state);
>
> used as the new state doesn't look ok to me. The above is the MST object's
> current SW state after an atomic commit/swap, but this isn't the new state a
> driver should program to the HW or pass to the drm helper functions. The
> object's current state could be ahead of what the driver should program to the
> HW, if the driver properly implements commit pipelining (so at the point
> you're programming a state you'd have already future commits computed and
> queued up, each queued-up commit with its own state).
>
> So instead of the above mst_state the driver should pass down the
> drm_atomic_state to dm_helpers_dp_mst_write_payload_allocation_table()
> which should use that instead to get the MST state it should program or pass
> to the drm layer.
>
> > So the patch is trying to get the behavior of this helper function
> > back to what it used to be.
>
> The behavior before was actually broken and one reason for that was a
> confusion about what's stored in the new payload state. It's a mixture of
> old/current state (vc_start_slot) and new state (time_slots). So I don't think
> it's a good idea to add even more dependency on this semantic.
>
> I think the right solution for what this patch is about - remove the need for
> dm_helpers_construct_old_payload(), would be to pass down
> drm_atomic_state to
> dm_helpers_dp_mst_write_payload_allocation_table()
> based on the above.
>
> > And the main reason that I want to change the pass in parameter is
> > like what I mentioned previously. The commit manipulation could be a
> > mix of allocations and removements for the payload. And in the spec,
> > it also introduces examples to reduce or increase the payload
> > allocation. Although we're not using reduction/increment today, it
> > implicitly imposes the limitation to use them before calling the
> > removement helper function with the old state as the passed in
> > parameter. So I also want to remove the dependency by this patch.
> > Would like to know your thoughts about this.
>
> It's not clear what would be the benefit of changing a payload without
> removing it first. In any case, I think the right direction for the driver
> would be
> to meet the requirement to use the proper atomic state with the drm helper
> functions (not the object's current SW state) as described above.
Hi Imre,
Thanks for pointing that out and that was also one of my plan to refactor! But I
would take that as another patch to follow up and would like to align with you
the idea for this helper function itself more.
My concern is referring to the old state to remove the time slot is just not
generic
right for what the helper function shall accomplish. Even it doesn't bring
benefit
as you see, having old state as the input imposes limitation to drivers using
it which
is the downside that it brought. The limitation is like what I tried to explain
before.
For an instance, if one driver has compressed streams allocated in the previous
commit and wants to disable these streams at the current commit. It handles and
accomplishes the commit into two steps that firstly to disable dsc engine only
(which increases the time slot), and next disable the streams. Under this
design,
the old state can't represent the exact number of time slot that it want's to
remove
at the moment. For this case, I don't think drm_dp_remove_payload_part2 should
block the driver to use it since the driver doesn't do things wrong.
Conversely, it's
due to the helper function constrains the driver to use an inappropriate input.
And with or without my patch, the current payload allocation table (i.e.
vc_start_slot
In new state) and the time slot that this new state is going to set (i.e.
time_slots in
new state) are already both in the new state. I think the patch doesn't add
irrelevant
input for removing a payload as this helper function should do, because the
time slot
it should remove is the exact one in the payload table now, not the one
captured in
previous commit. So in contrast, refer to old state time slot is a bit
confusing to me
because it's not generic right. Would like to know your thought on this point.
Appreciate your time!
>
> > Thanks, Imre!
> >
> > >
> > > > Again, thanks for your feedback Imre!
> > > >
> > > > >
> > > > > > > > /* Remove local payload allocation */
> > > > > > > > list_for_each_entry(pos, &mst_state->payloads, next) {
> > > > > > > > - if (pos != new_payload && pos->vc_start_slot >
> new_payload-
> > > > > > > >vc_start_slot)
> > > > > > > > - pos->vc_start_slot -=
> > > > > > > > old_payload->time_slots;
> > > > > > > > + if (pos != payload && pos->vc_start_slot >
> > > > > > > > + payload-
> > > > > > > >vc_start_slot)
> > > > > > > > + pos->vc_start_slot -=
> > > > > > > > + time_slots_to_remove;
> > > > > > > > }
> > > > > > > > - new_payload->vc_start_slot = -1;
> > > > > > > > + payload->vc_start_slot = -1;
> > > > > > > >
> > > > > > > > mgr->payload_count--;
> > > > > > > > - mgr->next_start_slot -= old_payload->time_slots;
> > > > > > > > + mgr->next_start_slot -= time_slots_to_remove;
> > > > > > > >
> > > > > > > > - if (new_payload->delete)
> > > > > > > > - drm_dp_mst_put_port_malloc(new_payload->port);
> > > > > > > > + if (payload->delete)
> > > > > > > > + drm_dp_mst_put_port_malloc(payload->port);
> > > > > > > >
> > > > > > > > - new_payload->payload_allocation_status =
> > > > > > > DRM_DP_MST_PAYLOAD_ALLOCATION_NONE;
> > > > > > > > + payload->payload_allocation_status =
> > > > > > > > +DRM_DP_MST_PAYLOAD_ALLOCATION_NONE;
> > > > > > > > }
> > > > > >
> > > > > > --
> > > > > > Regards,
> > > > > > Wayne
> > > >
> > > > --
> > > > Regards,
> > > > Wayne
> > --
> > Regards,
> > Wayne
--
Regards,
Wayne
