[PATCH 07/15] drm/i915/psr: Add function to compute max link-wake latency
Nautiyal, Ankit K
ankit.k.nautiyal at intel.com
Tue Aug 5 06:27:44 UTC 2025
On 8/5/2025 2:24 AM, Jani Nikula wrote:
> On Mon, 04 Aug 2025, Ankit Nautiyal <ankit.k.nautiyal at intel.com> wrote:
>> Introduce a helper to compute the max link wake latency when using
>> Auxless/Aux wake mechanism for PSR/Panel Replay/LOBF features.
>>
>> This will be used to compute the minimum guardband so that the link wake
>> latencies are accounted and these features work smoothly for higher
>> refresh rate panels.
>>
>> Bspec: 70151, 71477
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
>> ---
>> drivers/gpu/drm/i915/display/intel_psr.c | 64 ++++++++++++++++++++++++
>> drivers/gpu/drm/i915/display/intel_psr.h | 3 ++
>> 2 files changed, 67 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_psr.c b/drivers/gpu/drm/i915/display/intel_psr.c
>> index 6bd3454bb00e..6cdaff3ccc9f 100644
>> --- a/drivers/gpu/drm/i915/display/intel_psr.c
>> +++ b/drivers/gpu/drm/i915/display/intel_psr.c
>> @@ -33,6 +33,7 @@
>> #include "intel_atomic.h"
>> #include "intel_crtc.h"
>> #include "intel_cursor_regs.h"
>> +#include "intel_cx0_phy.h"
>> #include "intel_ddi.h"
>> #include "intel_de.h"
>> #include "intel_display_irq.h"
>> @@ -4249,3 +4250,66 @@ bool intel_psr_needs_alpm_aux_less(struct intel_dp *intel_dp,
>> {
>> return intel_dp_is_edp(intel_dp) && crtc_state->has_panel_replay;
>> }
>> +
>> +static
>> +int intel_psr_compute_aux_wake_latency(struct intel_dp *intel_dp,
>> + struct intel_crtc_state *crtc_state)
>> +{
>> +#define TFW_EXIT_LATENCY_MS 20000
>> +#define FAST_WAKE_LATENCY_MS 12000 /* Preamble: 8us; PHY wake: 4us */
>> + struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
>> + int aux_wake_latency_us;
>> + int io_buffer_wake_ms;
>> +
>> + io_buffer_wake_ms = intel_encoder_is_c10phy(encoder) ? 9790 : 14790;
>> +
>> + aux_wake_latency_us =
>> + DIV_ROUND_UP(io_buffer_wake_ms + TFW_EXIT_LATENCY_MS + FAST_WAKE_LATENCY_MS, 1000);
> See https://lore.kernel.org/r/eeda84457c813151a3459a46a91946b4fbbb9e44@intel.com
Oops! I think I have messed up msecs and usecs in the calculations.
I have realized, part of these calculations are already there in
functions in intel_alpm.c which can be used here.
I will correct this and rework on the patch.
Thanks Jani, for pointing this out.
Regards,
Ankit
>
>> +
>> + return aux_wake_latency_us;
>> +}
>> +
>> +static
>> +int intel_psr_compute_auxless_latency(struct intel_crtc_state *crtc_state)
>> +{
>> +#define PHY_ESTABLISHMENT_PERIOD_MS 50000
>> +#define LFPS_PERIOD_MS 800
>> +#define SILENCE_MAX_MS 180
>> + int linkrate_mhz = crtc_state->port_clock / 1000;
>> + int clock_data_switch_ms;
>> + int auxless_latency_us;
>> + int time_ml_phy_lock_ms;
>> + int num_ml_phy_lock;
>> + /*
>> + * TPS4 length = 252
>> + * tML_PHY_LOCK = TPS4 Length * ( 10 / (Link Rate in MHz) )
>> + * Number ML_PHY_LOCK = ( 7 + CEILING(6.5us / tML_PHY_LOCK ) + 1)
>> + * t2 = Number ML_PHY_LOCK * tML_PHY_LOCK
>> + * tCDS term = 2 * t2
>> + * =>tCDS_term = 2 * (7 * (252 * (10 /linkrate))+6.5)
>> + */
>> + time_ml_phy_lock_ms = (1000 * 252 * 10) / linkrate_mhz;
>> + num_ml_phy_lock = 7 + DIV_ROUND_UP(6500 * 1000, time_ml_phy_lock_ms) / 1000 + 1;
>> + clock_data_switch_ms = 2 * time_ml_phy_lock_ms * num_ml_phy_lock;
>> +
>> + auxless_latency_us = (LFPS_PERIOD_MS + SILENCE_MAX_MS + PHY_ESTABLISHMENT_PERIOD_MS +
>> + clock_data_switch_ms) / 1000;
>> +
>> + return auxless_latency_us;
>> +}
>> +
>> +int intel_psr_compute_max_link_wake_latency(struct intel_dp *intel_dp,
>> + struct intel_crtc_state *crtc_state,
>> + bool assume_all_enabled)
>> +{
>> + int aux_wake_latency = 0;
>> + int auxless_latency = 0;
>> +
>> + if (assume_all_enabled || crtc_state->has_sel_update)
>> + auxless_latency = intel_psr_compute_aux_wake_latency(intel_dp, crtc_state);
>> +
>> + if (assume_all_enabled || crtc_state->has_panel_replay)
>> + aux_wake_latency = intel_psr_compute_auxless_latency(crtc_state);
>> +
>> + return max(auxless_latency, aux_wake_latency);
>> +}
>> diff --git a/drivers/gpu/drm/i915/display/intel_psr.h b/drivers/gpu/drm/i915/display/intel_psr.h
>> index 9b061a22361f..c58d29620b49 100644
>> --- a/drivers/gpu/drm/i915/display/intel_psr.h
>> +++ b/drivers/gpu/drm/i915/display/intel_psr.h
>> @@ -81,5 +81,8 @@ void intel_psr_debugfs_register(struct intel_display *display);
>> bool intel_psr_needs_alpm(struct intel_dp *intel_dp, const struct intel_crtc_state *crtc_state);
>> bool intel_psr_needs_alpm_aux_less(struct intel_dp *intel_dp,
>> const struct intel_crtc_state *crtc_state);
>> +int intel_psr_compute_max_link_wake_latency(struct intel_dp *intel_dp,
>> + struct intel_crtc_state *crtc_state,
>> + bool assume_all_enabled);
>>
>> #endif /* __INTEL_PSR_H__ */
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