[PATCH 3/3] drm/mst: adjust the function drm_dp_remove_payload_part2()
Lin, Wayne
Wayne.Lin at amd.com
Tue Sep 12 07:26:29 UTC 2023
[Public]
> -----Original Message-----
> From: Imre Deak <imre.deak at intel.com>
> Sent: Saturday, September 9, 2023 3:18 AM
> To: Lin, Wayne <Wayne.Lin at amd.com>
> Cc: dri-devel at lists.freedesktop.org; amd-gfx at lists.freedesktop.org;
> lyude at redhat.com; jani.nikula at intel.com; ville.syrjala at linux.intel.com;
> Wentland, Harry <Harry.Wentland at amd.com>; Zuo, Jerry
> <Jerry.Zuo at amd.com>
> Subject: Re: [PATCH 3/3] drm/mst: adjust the function
> drm_dp_remove_payload_part2()
>
> On Thu, Sep 07, 2023 at 03:44:39AM +0000, Lin, Wayne wrote:
> > [AMD Official Use Only - General]
> >
> > > -----Original Message-----
> > > From: Imre Deak <imre.deak at intel.com>
> > > Sent: Friday, August 25, 2023 9:56 PM
> > > To: Lin, Wayne <Wayne.Lin at amd.com>
> > > Cc: dri-devel at lists.freedesktop.org; amd-gfx at lists.freedesktop.org;
> > > lyude at redhat.com; jani.nikula at intel.com;
> > > ville.syrjala at linux.intel.com; Wentland, Harry
> > > <Harry.Wentland at amd.com>; Zuo, Jerry <Jerry.Zuo at 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.deak at intel.com>
> > > > > Sent: Saturday, August 19, 2023 1:46 AM
> > > > > To: Lin, Wayne <Wayne.Lin at amd.com>
> > > > > Cc: dri-devel at lists.freedesktop.org;
> > > > > amd-gfx at lists.freedesktop.org; lyude at redhat.com;
> > > > > jani.nikula at intel.com; ville.syrjala at linux.intel.com; Wentland,
> > > > > Harry <Harry.Wentland at amd.com>; Zuo, Jerry <Jerry.Zuo at 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.deak at intel.com>
> > > > > > > Sent: Tuesday, August 8, 2023 12:00 AM
> > > > > > > To: Lin, Wayne <Wayne.Lin at amd.com>
> > > > > > > Cc: dri-devel at lists.freedesktop.org;
> > > > > > > amd-gfx at lists.freedesktop.org; lyude at redhat.com;
> > > > > > > jani.nikula at intel.com; ville.syrjala at linux.intel.com;
> > > > > > > Wentland, Harry <Harry.Wentland at amd.com>; Zuo, Jerry
> > > > > > > <Jerry.Zuo at 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.deak at intel.com>
> > > > > > > > > Sent: Friday, August 4, 2023 11:32 PM
> > > > > > > > > To: Lin, Wayne <Wayne.Lin at amd.com>
> > > > > > > > > Cc: dri-devel at lists.freedesktop.org;
> > > > > > > > > amd-gfx at lists.freedesktop.org; lyude at redhat.com;
> > > > > > > > > jani.nikula at intel.com; ville.syrjala at linux.intel.com;
> > > > > > > > > Wentland, Harry <Harry.Wentland at amd.com>; Zuo, Jerry
> > > > > > > > > <Jerry.Zuo at 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!
>
> I'd like to be sure that the payload is removed with the size it was added with
> in the previous commit and as I wrote above not depend for this on the new
> payload state with a mixture of old/current/new states.
> Based on that I'd be ok for instance with a new
>
> int drm_dp_remove_port_payload(mgr, mst_state, port)
>
> function which looks up / removes the payload with the time_slots calculated
> based on the payload table as in your patch and returns the calculated
> time_slots.
>
> The AMD driver could call the above function and the current
> drm_dp_remove_payload(mgr, mst_state, old_payload) function would be
>
> time_slots = drm_dp_remove_port_payload(mgr, mst_state,
> old_payload->port);
> WARN_ON(time_slots != old_payload->time_slots);
>
> --Imre
Sorry but I might not fully understand what you suggested here. Would like to know
if you agree on referring to the time slot number of the payload table at the moment
is better then referring old_payload->time_slots for drm_dp_remove_payload()? If
you agree on that, my patch actually is just replacing old_payload->time_slots with
the more appropriate one. Not adding mixture of old/current but replacing the old
with the current one. And like what I explained in previous example, when calling
drm_dp_remove_payload(), the time slot number to be removed shouldn't be
constrained to the one in previous commit. The number in the payload table when
we're about to remove the payload might be a better choice. Could you elaborate
more what's the mixture that this patch is adding on, please?
As for the changing suggestion, are you suggesting to create a new function
drm_dp_remove_port_payload() to wrap up the calculation in my patch? If so, I think
that's the consensus to use current time slot number to replace the one in old_payload.
Therefore, it doesn't have to pass old_payload to drm_dp_remove_port_payload(), and
"WARN_ON(time_slots != old_payload->time_slots);" is not appropriate as for the
example that I gave previously.
Thanks for helping me out here.
--
Regards,
Wayne
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