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_DP_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.
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) {
