[PATCH 1/3] drm/i915/pps: Add helpers to lock PPS for AUX transfers
Jani Nikula
jani.nikula at linux.intel.com
Mon Mar 24 13:59:50 UTC 2025
On Mon, 24 Mar 2025, Imre Deak <imre.deak at intel.com> wrote:
> On Mon, Mar 24, 2025 at 02:28:35PM +0200, Jani Nikula wrote:
>> On Mon, 24 Mar 2025, Imre Deak <imre.deak at intel.com> wrote:
>> > On Mon, Mar 24, 2025 at 12:33:22PM +0200, Jani Nikula wrote:
>> >> On Fri, 21 Mar 2025, Imre Deak <imre.deak at intel.com> wrote:
>> >> > Factor out from the DP AUX transfer function the logic to lock/unlock
>> >> > the Panel Power Sequencer state and enable/disable the VDD power
>> >> > required for the AUX transfer, adding these to helpers in intel_pps.c .
>> >> > This prepares for a follow-up change making these steps dependent on the
>> >> > platform and output type.
>> >> >
>> >> > Signed-off-by: Imre Deak <imre.deak at intel.com>
>> >> > ---
>> >> > drivers/gpu/drm/i915/display/intel_dp_aux.c | 16 ++----------
>> >> > drivers/gpu/drm/i915/display/intel_pps.c | 29 ++++++++++++++++++++-
>> >> > drivers/gpu/drm/i915/display/intel_pps.h | 3 ++-
>> >> > 3 files changed, 32 insertions(+), 16 deletions(-)
>> >> >
>> >> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
>> >> > index ec27bbd70bcf0..bf5ccfa24ca0b 100644
>> >> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
>> >> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
>> >> > @@ -272,15 +272,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>> >> > aux_domain = intel_aux_power_domain(dig_port);
>> >> >
>> >> > aux_wakeref = intel_display_power_get(display, aux_domain);
>> >> > - pps_wakeref = intel_pps_lock(intel_dp);
>> >> > -
>> >> > - /*
>> >> > - * We will be called with VDD already enabled for dpcd/edid/oui reads.
>> >> > - * In such cases we want to leave VDD enabled and it's up to upper layers
>> >> > - * to turn it off. But for eg. i2c-dev access we need to turn it on/off
>> >> > - * ourselves.
>> >> > - */
>> >> > - vdd = intel_pps_vdd_on_unlocked(intel_dp);
>> >> > + pps_wakeref = intel_pps_lock_for_aux(intel_dp, &vdd);
>> >> >
>> >> > /*
>> >> > * dp aux is extremely sensitive to irq latency, hence request the
>> >> > @@ -289,8 +281,6 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>> >> > */
>> >> > cpu_latency_qos_update_request(&intel_dp->pm_qos, 0);
>> >> >
>> >> > - intel_pps_check_power_unlocked(intel_dp);
>> >> > -
>> >> > /*
>> >> > * FIXME PSR should be disabled here to prevent
>> >> > * it using the same AUX CH simultaneously
>> >> > @@ -427,10 +417,8 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>> >> > out:
>> >> > cpu_latency_qos_update_request(&intel_dp->pm_qos, PM_QOS_DEFAULT_VALUE);
>> >> >
>> >> > - if (vdd)
>> >> > - intel_pps_vdd_off_unlocked(intel_dp, false);
>> >> > + intel_pps_unlock_for_aux(intel_dp, pps_wakeref, vdd);
>> >> >
>> >> > - intel_pps_unlock(intel_dp, pps_wakeref);
>> >> > intel_display_power_put_async(display, aux_domain, aux_wakeref);
>> >> > out_unlock:
>> >> > intel_digital_port_unlock(encoder);
>> >> > diff --git a/drivers/gpu/drm/i915/display/intel_pps.c b/drivers/gpu/drm/i915/display/intel_pps.c
>> >> > index 617ce49931726..3c078fd53fbfa 100644
>> >> > --- a/drivers/gpu/drm/i915/display/intel_pps.c
>> >> > +++ b/drivers/gpu/drm/i915/display/intel_pps.c
>> >> > @@ -571,7 +571,7 @@ static bool edp_have_panel_vdd(struct intel_dp *intel_dp)
>> >> > return intel_de_read(display, _pp_ctrl_reg(intel_dp)) & EDP_FORCE_VDD;
>> >> > }
>> >> >
>> >> > -void intel_pps_check_power_unlocked(struct intel_dp *intel_dp)
>> >> > +static void intel_pps_check_power_unlocked(struct intel_dp *intel_dp)
>> >> > {
>> >> > struct intel_display *display = to_intel_display(intel_dp);
>> >> > struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
>> >> > @@ -955,6 +955,33 @@ void intel_pps_vdd_off(struct intel_dp *intel_dp)
>> >> > intel_pps_vdd_off_unlocked(intel_dp, false);
>> >> > }
>> >> >
>> >> > +intel_wakeref_t intel_pps_lock_for_aux(struct intel_dp *intel_dp, bool *vdd_ref)
>> >> > +{
>> >> > + intel_wakeref_t wakeref;
>> >> > +
>> >> > + wakeref = intel_pps_lock(intel_dp);
>> >> > +
>> >> > + /*
>> >> > + * We will be called with VDD already enabled for dpcd/edid/oui reads.
>> >> > + * In such cases we want to leave VDD enabled and it's up to upper layers
>> >> > + * to turn it off. But for eg. i2c-dev access we need to turn it on/off
>> >> > + * ourselves.
>> >> > + */
>> >> > + *vdd_ref = intel_pps_vdd_on_unlocked(intel_dp);
>> >> > +
>> >> > + intel_pps_check_power_unlocked(intel_dp);
>> >> > +
>> >> > + return wakeref;
>> >> > +}
>> >> > +
>> >> > +void intel_pps_unlock_for_aux(struct intel_dp *intel_dp, intel_wakeref_t wakeref, bool vdd_ref)
>> >> > +{
>> >> > + if (vdd_ref)
>> >> > + intel_pps_vdd_off_unlocked(intel_dp, false);
>> >> > +
>> >> > + intel_pps_unlock(intel_dp, wakeref);
>> >> > +}
>> >>
>> >> It took me a while to pinpoint what exactly I don't like about this
>> >> interface.
>> >>
>> >> And I mean the whole intel_pps.h interface is already really difficult
>> >> to understand.
>> >>
>> >> This flips the lock/unlock and vdd on/off logic inside out.
>> >>
>> >> Normally you have functions for doing vdd or power or backlight, or
>> >> anything PPS really, and they're either unlocked (assuming the caller
>> >> handles PPS lock) or locked (the function itself takes the lock).
>> >
>> > The PPS and VDD handling steps are dependent (PPS must be locked for
>> > enabling VDD) and both are skipped for the same reason during AUX
>> > transfers. So I thought it makes sense to move these to a separate
>> > function and skip both based on the same platform/output type check.
>>
>> On the contrary, I think the reasons are different.
>>
>> VDD is only needed for eDP.
>>
>> The PPS must be locked for VDD change (IOW for eDP) and for VLV/CHV pipe
>> based PPS. But these two cases are independent.
>
> The case requiring VDD (eDP) is a subset of the cases requring PPS to be
> locked (eDP or VLV/CHV). These are not independent cases.
Logically, they are. VLV/CHV requires the PPS lock also for
non-eDP. It's not a subset.
BR,
Jani.
>
>> >> This one purports to be an interface for lock/unlock, but in reality it
>> >> also does VDD internally. And that feels really quite wrong to me.
>> >>
>> >> ---
>> >>
>> >> These are a single-use interface that I think make intel_pps.[ch] more
>> >> difficult to understand. I'd suggest checking how you'd implement this
>> >> logic inside intel_dp_aux_xfer() *without* changing the intel_pps.[ch]
>> >> interface at all.
>> >>
>> >> Okay, took a quick stab at it, and unless I'm missing something it's
>> >> super easy:
>> >
>> > I still think it'd be better to have a separate function for both
>> > locking PPS and enabling VDD for the reason I described above, that is
>> > to clarify that the PPS state must be locked to enable VDD.
>>
>> But there's no requirement that they must be done at the same time.
>
> There is also no reason not do them at the same time for AUX. A benefit
> of doing that would be to clarify the dependency of VDD on PPS and also
> simplify intel_dp_aux_xfer().
>
>> The PPS lock could be held for a much longer period or for other
>> things than just VDD. And in this case, the PPS lock may indeed
>> protect *other* things than just VDD. Adding the separate function
>> ties these unrelated cases together for IMO not good enough reason.
>> intel_pps_vdd_on_unlocked() does check that it's called with the PPS
>> lock held.
>>
>> But I realize it needs to be relaxed a bit like this:
>
> Yes, noticed this too. It was one reason I opted for skipping PPS
> locking / VDD enabling from one spot.
>
>> diff --git a/drivers/gpu/drm/i915/display/intel_pps.c b/drivers/gpu/drm/i915/display/intel_pps.c
>> index 617ce4993172..c883e872c9c8 100644
>> --- a/drivers/gpu/drm/i915/display/intel_pps.c
>> +++ b/drivers/gpu/drm/i915/display/intel_pps.c
>> @@ -744,11 +744,11 @@ bool intel_pps_vdd_on_unlocked(struct intel_dp *intel_dp)
>> i915_reg_t pp_stat_reg, pp_ctrl_reg;
>> bool need_to_disable = !intel_dp->pps.want_panel_vdd;
>>
>> - lockdep_assert_held(&display->pps.mutex);
>> -
>> if (!intel_dp_is_edp(intel_dp))
>> return false;
>>
>> + lockdep_assert_held(&display->pps.mutex);
>> +
>> cancel_delayed_work(&intel_dp->pps.panel_vdd_work);
>> intel_dp->pps.want_panel_vdd = true;
>>
>> @@ -925,11 +925,11 @@ void intel_pps_vdd_off_unlocked(struct intel_dp *intel_dp, bool sync)
>> {
>> struct intel_display *display = to_intel_display(intel_dp);
>>
>> - lockdep_assert_held(&display->pps.mutex);
>> -
>> if (!intel_dp_is_edp(intel_dp))
>> return;
>>
>> + lockdep_assert_held(&display->pps.mutex);
>> +
>> INTEL_DISPLAY_STATE_WARN(display, !intel_dp->pps.want_panel_vdd,
>> "[ENCODER:%d:%s] %s VDD not forced on",
>> dp_to_dig_port(intel_dp)->base.base.base.id,
>>
>>
>> > I guess the above could be done separately later in any case, so I can
>> > inline the fix as you suggest.
>> >
>> >> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
>> >> index ec27bbd70bcf..a5608659df59 100644
>> >> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
>> >> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
>> >> @@ -247,7 +247,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>> >> u32 aux_clock_divider;
>> >> enum intel_display_power_domain aux_domain;
>> >> intel_wakeref_t aux_wakeref;
>> >> - intel_wakeref_t pps_wakeref;
>> >> + intel_wakeref_t pps_wakeref = NULL;
>> >> int i, ret, recv_bytes;
>> >> int try, clock = 0;
>> >> u32 status;
>> >> @@ -272,7 +272,10 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>> >> aux_domain = intel_aux_power_domain(dig_port);
>> >>
>> >> aux_wakeref = intel_display_power_get(display, aux_domain);
>> >> - pps_wakeref = intel_pps_lock(intel_dp);
>> >> +
>> >> + if (intel_dp_is_edp(intel_dp) ||
>> >> + (display->platform.valleyview || display->platform.cherryview))
>> >> + pps_wakeref = intel_pps_lock(intel_dp);
>> >>
>> >> /*
>> >> * We will be called with VDD already enabled for dpcd/edid/oui reads.
>> >> @@ -430,7 +433,8 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>> >> if (vdd)
>> >> intel_pps_vdd_off_unlocked(intel_dp, false);
>> >>
>> >> - intel_pps_unlock(intel_dp, pps_wakeref);
>> >> + if (pps_wakeref)
>> >> + intel_pps_unlock(intel_dp, pps_wakeref);
>> >> intel_display_power_put_async(display, aux_domain, aux_wakeref);
>> >> out_unlock:
>> >> intel_digital_port_unlock(encoder);
>> >>
>> >>
>> >> Please let's not make intel_pps.[ch] harder to understand.
>> >>
>> >>
>> >> BR,
>> >> Jani.
>> >>
>> >>
>> >> > +
>> >> > void intel_pps_on_unlocked(struct intel_dp *intel_dp)
>> >> > {
>> >> > struct intel_display *display = to_intel_display(intel_dp);
>> >> > diff --git a/drivers/gpu/drm/i915/display/intel_pps.h b/drivers/gpu/drm/i915/display/intel_pps.h
>> >> > index c83007152f07d..4390d05892325 100644
>> >> > --- a/drivers/gpu/drm/i915/display/intel_pps.h
>> >> > +++ b/drivers/gpu/drm/i915/display/intel_pps.h
>> >> > @@ -31,10 +31,11 @@ bool intel_pps_vdd_on_unlocked(struct intel_dp *intel_dp);
>> >> > void intel_pps_vdd_off_unlocked(struct intel_dp *intel_dp, bool sync);
>> >> > void intel_pps_on_unlocked(struct intel_dp *intel_dp);
>> >> > void intel_pps_off_unlocked(struct intel_dp *intel_dp);
>> >> > -void intel_pps_check_power_unlocked(struct intel_dp *intel_dp);
>> >> >
>> >> > void intel_pps_vdd_on(struct intel_dp *intel_dp);
>> >> > void intel_pps_vdd_off(struct intel_dp *intel_dp);
>> >> > +intel_wakeref_t intel_pps_lock_for_aux(struct intel_dp *intel_dp, bool *vdd_ref);
>> >> > +void intel_pps_unlock_for_aux(struct intel_dp *intel_dp, intel_wakeref_t wakeref, bool vdd_ref);
>> >> > void intel_pps_on(struct intel_dp *intel_dp);
>> >> > void intel_pps_off(struct intel_dp *intel_dp);
>> >> > void intel_pps_vdd_off_sync(struct intel_dp *intel_dp);
>> >>
>> >> --
>> >> Jani Nikula, Intel
>>
>> --
>> Jani Nikula, Intel
--
Jani Nikula, Intel
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