> -----Original Message-----
> From: Hogander, Jouni <[email protected]>
> Sent: Tuesday, September 29, 2026 12:30 PM
> To: [email protected]; [email protected]; Manna,
> Animesh <[email protected]>; [email protected]
> Cc: Kandpal, Suraj <[email protected]>; Nikula, Jani
> <[email protected]>
> Subject: Re: [PATCH v6 08/18] drm/i915/alpm: table based establishment
> period
>
> On Tue, 2026-09-15 at 23:34 +0530, Animesh Manna wrote:
> > Only use the table when the link rate is listed (idx valid) and the
> > LTTPR count is within the table bounds. A zero entry means the rate
> > has no tabulated value, so fall back to the computed establishment
> > period below.
> >
> > Note: The table and its values are taken from DP2.1 vesa spec.
> >
> > v2: Add check for negative error codes from drm_dp_lttpr_count().
> > [sashiko]
> >
> > Cc: Jouni Högander <[email protected]>
> > Signed-off-by: Animesh Manna <[email protected]>
> > ---
> > drivers/gpu/drm/i915/display/intel_alpm.c | 95
> > +++++++++++++++++++++++
> > 1 file changed, 95 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c
> > b/drivers/gpu/drm/i915/display/intel_alpm.c
> > index dc025058a626..cb24bba801a1 100644
> > --- a/drivers/gpu/drm/i915/display/intel_alpm.c
> > +++ b/drivers/gpu/drm/i915/display/intel_alpm.c
> > @@ -122,6 +122,92 @@ static int get_dp_link_symbol_size(const struct
> > intel_crtc_state *crtc_state)
> > return intel_dp_is_uhbr(crtc_state) ? 32 : 10;
> > }
> >
> > +#define DEFAULT_MAX_LTTPR_COUNT 7
> > +#define MAX_SUPPORTED_DP_LINK_RATES 12
> > +
> > +static const u32
> >
> establishment_periods[DEFAULT_MAX_LTTPR_COUNT][MAX_SUPPORTED_D
> P_LINK_
> > RATES] = {
> > + /* 1620, 2160, 2430, 2700, 3240, 4320, 5400, 6750, 8100,
> > 10000, 13500, 20000 */
> > + /* No Retimers */
> > + { 61070, 0, 0, 56710, 0, 0, 53450, 0, 52360, 59050, 56750,
> > 54620 },
> > + /* 1 Retimer */
> > + { 155670, 0, 0, 151310, 0, 0, 148050, 0, 146960, 153650,
> > 151350, 149220 },
> > + /* 2 Retimers */
> > + { 181160, 0, 0, 172450, 0, 0, 165910, 0, 163740, 177120,
> > 172520, 168220 },
> > + /* 3 Retimers */
> > + { 206650, 0, 0, 193580, 0, 0, 183780, 0, 180510, 200590,
> > 193690, 187290 },
> > + /* 4 Retimers */
> > + { 232140, 0, 0, 214710, 0, 0, 201650, 0, 197290, 224060,
> > 214860, 206320 },
> > + /* 5 Retimers */
> > + { 257620, 0, 0, 235850, 0, 0, 219510, 0, 214070, 247530,
> > 236030, 225360 },
> > + /* 6 Retimers */
> > + { 283110, 0, 0, 256980, 0, 0, 237380, 0, 230850, 271000,
> > 257200, 244390 },
> > +};
> > +
> > +enum link_rate_idx {
> > + LINK_RATE_INVALID = -1,
> > + LINK_RATE_1,
> > + LINK_RATE_2,
> > + LINK_RATE_3,
> > + LINK_RATE_4,
> > + LINK_RATE_5,
> > + LINK_RATE_6,
> > + LINK_RATE_7,
> > + LINK_RATE_8,
> > + LINK_RATE_9,
> > + LINK_RATE_10,
> > + LINK_RATE_11,
> > + LINK_RATE_12
> > +};
> > +
> > +static int get_link_rate_index(int port_clock) {
> > + int link_rate_index;
> > +
> > + switch (port_clock) {
> > + case 162000:
> > + link_rate_index = LINK_RATE_1; // Rate_1 (RBR) -
> > 1.62 Gbps/Lane
> > + break;
> > + case 216000:
> > + link_rate_index = LINK_RATE_2; // Rate_2 -
> > 2.16 Gbps/Lane
> > + break;
> > + case 243000:
> > + link_rate_index = LINK_RATE_3; // Rate_3 -
> > 2.43 Gbps/Lane
> > + break;
> > + case 270000:
> > + link_rate_index = LINK_RATE_4; // Rate_4 (HBR) -
> > 2.70 Gbps/Lane
> > + break;
> > + case 324000:
> > + link_rate_index = LINK_RATE_5; // Rate_5 (RBR2)-
> > 3.24 Gbps/Lane
> > + break;
> > + case 432000:
> > + link_rate_index = LINK_RATE_6; // Rate_6 -
> > 4.32 Gbps/Lane
> > + break;
> > + case 540000:
> > + link_rate_index = LINK_RATE_7; // Rate_7 (HBR2)-
> > 5.40 Gbps/Lane
> > + break;
> > + case 675000:
> > + link_rate_index = LINK_RATE_8; // Rate_8 -
> > 6.75 Gbps/Lane
> > + break;
> > + case 810000:
> > + link_rate_index = LINK_RATE_9; // Rate_9 (HBR3)-
> > 8.10 Gbps/Lane
> > + break;
> > + case 1000000:
> > + link_rate_index = LINK_RATE_10; // Rate_10
> > (UHBR10) - 10.0 Gbps/Lane
> > + break;
> > + case 1350000:
> > + link_rate_index = LINK_RATE_11; // Rate_11
> > (UHBR13.5) - 13.5 Gbps/Lane
> > + break;
> > + case 2000000:
> > + link_rate_index = LINK_RATE_12; // Rate_12
> > (UHBR20) - 20.0 Gbps/Lane
> > + break;
> > + default:
> > + link_rate_index = LINK_RATE_INVALID;
> > + break;
> > + }
> > +
> > + return link_rate_index;
> > +}
>
> Difference between what this table is giving us and what we are getting from
> the formula is coming from SILENCE_PERIOD_TIME and tlfps_period.
> In DP spec they are using max values while our calculation is using midpoint.
>
> I think we could just switch to max values on these and drop adding tables
> completely.
As per I know the formula-based approach with max values also little short from
the values coming from Vesa spec. This is found little sensitive during ALPM
testing on specific test setup and resulting flip-done timeout. To overcome the
issue currently prefer to direct values from vesa spec. And if not present will
fallback to formula based approach.
Regards,
Animesh
>
> BR,
> Jouni Högander
>
> > +
> > static int get_establishment_period(struct intel_dp *intel_dp,
> > const struct intel_crtc_state
> > *crtc_state)
> > {
> > @@ -138,8 +224,17 @@ static int get_establishment_period(struct
> > intel_dp *intel_dp,
> > if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_EDP)) {
> > tcds = (7 + DIV_ROUND_UP(6500, tml_phy_lock) + 1) *
> tml_phy_lock;
> > } else {
> > + int idx = get_link_rate_index(crtc_state-
> > >port_clock);
> > +
> > tcds = 7 * tml_phy_lock;
> > lttpr_count = drm_dp_lttpr_count(intel_dp-
> > >lttpr_common_caps);
> > +
> > + if (idx != LINK_RATE_INVALID && lttpr_count >= 0 &&
> > + lttpr_count < DEFAULT_MAX_LTTPR_COUNT &&
> > + establishment_periods[lttpr_count][idx]) {
> > + establishment_period =
> > establishment_periods[lttpr_count][idx];
> > + return establishment_period;
> > + }
> > }
> >
> > if (lttpr_count > 0) {
