On Tue, 10 Jun 2025, "Nautiyal, Ankit K" <[email protected]> wrote: > On 6/10/2025 5:52 PM, Jani Nikula wrote: >> On Tue, 10 Jun 2025, Ankit Nautiyal <[email protected]> wrote: >>> Some ICL/TGL platforms with combo PHY ports can theoretically support HBR3, >>> but in practice, signal integrity issues may prevent stable operation. >>> While some systems include a Parade PS8461 mux chip to mitigate jitter and >>> enable HBR3, there is no reliable way to detect its presence. >>> Additionally, many systems have broken or missing VBT entries, making it >>> unsafe to rely on VBT for link rate limits. >>> >>> To address this, introduce a new kernel parameter `limit_edp_hbr2`. >>> When set, this parameter forces the eDP link rate to be capped at >>> HBR2 (540000 kHz), overriding any higher advertised rates from the sink or >>> DPCD. By default, the higher rates will be allowed, i.e. the parameter >>> will be set to false. >>> >>> This provides a manual override for users and OEMs to limit the rate to >>> HBR2, where output with HBR3 is unstable. >> I'm afraid a module parameter is not an acceptable solution. >> >> Have I missed a discussion why a quirk is not possible? > > The problem I was facing was that the OUI details are available from the > logs in gitlab issue 5969 [1], but the DEVICE_ID field was blank so I > had used DEVICE_ID_ANY. > > + /* Novatek panel */ > + { OUI(0x38, 0xEC, 0x11), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_HBR3) > }, > > But with this, the HBR3 rate might get removed for many panels with same > OUI, as I had mentioned in [3]. > > Also I feel the issue might not be specific to the panel but perhaps to > few skus with low voltage combo phy ports. > > But we cannot rely on the low voltage sku check as OEMs are expected to > limit the rate via VBTs. It seems VBTs are also sometimes not correct. > > You have briefly highlighted the problem in comments in gitlab issue > 5969 [2]. > > So I was thinking if we can give a knob to limit the rate.
It has to work out of the box. Module parameters might be handy for us, but not the users. > Can we add a quirk for machine/model/vendor to limit the rate for > specific machines? Yes, if that's the common denominator. BR, Jani. > > > [1] https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/5969 > > [2] > https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/5969#note_2309988 > > [3] https://patchwork.freedesktop.org/patch/654704/?series=149227&rev=1 > > > Regards, > > Ankit > >> >> >> BR, >> Jani. >> >>> Signed-off-by: Ankit Nautiyal <[email protected]> >>> --- >>> .../drm/i915/display/intel_display_params.c | 2 + >>> .../drm/i915/display/intel_display_params.h | 1 + >>> drivers/gpu/drm/i915/display/intel_dp.c | 50 ++++++++++++++++--- >>> 3 files changed, 46 insertions(+), 7 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/i915/display/intel_display_params.c >>> b/drivers/gpu/drm/i915/display/intel_display_params.c >>> index c4f1ab43fc0c..84f36104f5ca 100644 >>> --- a/drivers/gpu/drm/i915/display/intel_display_params.c >>> +++ b/drivers/gpu/drm/i915/display/intel_display_params.c >>> @@ -133,6 +133,8 @@ intel_display_param_named_unsafe(enable_dmc_wl, int, >>> 0400, >>> "(-1=use per-chip default, 0=disabled, 1=enabled, 2=match any register, >>> 3=always locked) " >>> "Default: -1"); >>> >>> +intel_display_param_named(limit_edp_hbr2, bool, 0400, "Limit EDP link rate >>> to HBR2 (default: false)"); >>> + >>> __maybe_unused >>> static void _param_print_bool(struct drm_printer *p, const char >>> *driver_name, >>> const char *name, bool val) >>> diff --git a/drivers/gpu/drm/i915/display/intel_display_params.h >>> b/drivers/gpu/drm/i915/display/intel_display_params.h >>> index 5317138e6044..f7ba9805f97f 100644 >>> --- a/drivers/gpu/drm/i915/display/intel_display_params.h >>> +++ b/drivers/gpu/drm/i915/display/intel_display_params.h >>> @@ -48,6 +48,7 @@ struct drm_printer; >>> param(bool, psr_safest_params, false, 0400) \ >>> param(bool, enable_psr2_sel_fetch, true, 0400) \ >>> param(int, enable_dmc_wl, -1, 0400) \ >>> + param(bool, limit_edp_hbr2, false, 0400) \ >>> >>> #define MEMBER(T, member, ...) T member; >>> struct intel_display_params { >>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c >>> b/drivers/gpu/drm/i915/display/intel_dp.c >>> index 2a0b76ae33cd..85022e5e64f4 100644 >>> --- a/drivers/gpu/drm/i915/display/intel_dp.c >>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c >>> @@ -174,10 +174,29 @@ int intel_dp_link_symbol_clock(int rate) >>> >>> static int max_dprx_rate(struct intel_dp *intel_dp) >>> { >>> + struct intel_display *display = to_intel_display(intel_dp); >>> + struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; >>> + int max_rate; >>> + >>> if (intel_dp_tunnel_bw_alloc_is_enabled(intel_dp)) >>> - return drm_dp_tunnel_max_dprx_rate(intel_dp->tunnel); >>> + max_rate = drm_dp_tunnel_max_dprx_rate(intel_dp->tunnel); >>> + else >>> + max_rate = >>> drm_dp_bw_code_to_link_rate(intel_dp->dpcd[DP_MAX_LINK_RATE]); >>> >>> - return drm_dp_bw_code_to_link_rate(intel_dp->dpcd[DP_MAX_LINK_RATE]); >>> + /* >>> + * Some platforms with combo PHY ports may not reliably support HBR3 >>> + * due to signal integrity limitations, despite advertising it. >>> + * If the kernel parameter `limit_edp_hbr2` is set, cap the link >>> + * rate to HBR2 to avoid unstable configurations. >>> + */ >>> + if (max_rate >= 810000 && display->params.limit_edp_hbr2) { >>> + drm_dbg_kms(display->drm, >>> + "[ENCODER:%d:%s] Forcing max link rate to HBR2 due >>> to limit_edp_hbr2 set\n", >>> + encoder->base.base.id, encoder->base.name); >>> + max_rate = 540000; >>> + } >>> + >>> + return max_rate; >>> } >>> >>> static int max_dprx_lane_count(struct intel_dp *intel_dp) >>> @@ -4253,6 +4272,9 @@ static void intel_edp_mso_init(struct intel_dp >>> *intel_dp) >>> static void >>> intel_edp_set_sink_rates(struct intel_dp *intel_dp) >>> { >>> + struct intel_display *display = to_intel_display(intel_dp); >>> + struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; >>> + >>> intel_dp->num_sink_rates = 0; >>> >>> if (intel_dp->edp_dpcd[0] >= DP_EDP_14) { >>> @@ -4263,10 +4285,7 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp) >>> sink_rates, sizeof(sink_rates)); >>> >>> for (i = 0; i < ARRAY_SIZE(sink_rates); i++) { >>> - int val = le16_to_cpu(sink_rates[i]); >>> - >>> - if (val == 0) >>> - break; >>> + int rate; >>> >>> /* Value read multiplied by 200kHz gives the per-lane >>> * link rate in kHz. The source rates are, however, >>> @@ -4274,7 +4293,24 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp) >>> * back to symbols is >>> * (val * 200kHz)*(8/10 ch. encoding)*(1/8 bit to Byte) >>> */ >>> - intel_dp->sink_rates[i] = (val * 200) / 10; >>> + rate = le16_to_cpu(sink_rates[i]) * 200 / 10; >>> + >>> + if (rate == 0) >>> + break; >>> + >>> + /* >>> + * Some platforms cannot reliably drive HBR3 rates due >>> to PHY limitations, >>> + * even if the sink advertises support. If kernel >>> parameter `limit_edp_hbr2` >>> + * is set, reject any sink rates above HBR2 to ensure >>> stable operation. >>> + */ >>> + if (rate >= 810000 && display->params.limit_edp_hbr2) { >>> + drm_dbg_kms(display->drm, >>> + "[ENCODER:%d:%s] Limit the rate to >>> HBR2 due to limit_edp_hbr2 param\n", >>> + encoder->base.base.id, >>> encoder->base.name); >>> + break; >>> + } >>> + >>> + intel_dp->sink_rates[i] = rate; >>> } >>> intel_dp->num_sink_rates = i; >>> } -- Jani Nikula, Intel
