drm_dp_downs...max_dotclock(9)

💅 drm_dp_downs...max_dotclock(9) — the kernel API manual, bestie edition

okay so this is a page from the Kernel API Manual (section 9, the kernel-API girlies) and it's all about drm_dp_downstream_max_dotclock. yes the title is truncated with dots, no that's not a typo, that's just how the header renders. we move.

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✨ NAME ✨

drm_dp_downstream_max_dotclock — extract downstream facing port max dot clock

like, it goes and gets the max dot clock for you. that's the whole job. slay.

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🌸 SYNOPSIS 🌸

int drm_dp_downstream_max_dotclock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
                                   const u8 port_cap[4]);

it returns an int, takes two const u8 arrays, and honestly? iconic signature. no notes.

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🎀 ARGUMENTS 🎀

• dpcd — DisplayPort configuration data. the whole vibe sheet for the DP thing, passed in as const u8 dpcd[DP_RECEIVER_CAP_SIZE].
• port_cap — port capabilities, given to us as a const u8 port_cap[4]. four bytes of pure potential bestie.

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💖 RETURN 💖

on success you get the downstream facing port max dot clock in kHz 🥳 — or 0 if the max clock isn't defined. that's it, that's the return. no cap.

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🦋 SEE ALSO 🦋

okay bestie sit down, this list is long and we are not skipping a single one, every single reference is coming with us 💅

first up, the file itself lives in the kernel at ./drivers/gpu/drm/display/drm_dp_helper.c — the dp helpers crew:

dp helpers(9), drm_dp_phy_name(9), drm_dp_lttpr_wake_timeout_setup(9), dp helpers(9) (yes it's in there a second time, we love a cameo ✨), drm_dp_dpcd_probe(9), drm_dp_dpcd_set_powered(9), drm_dp_dpcd_set_probe(9), drm_dp_dpcd_read(9), drm_dp_dpcd_write(9), drm_dp_dpcd_read_link_status(9), drm_dp_dpcd_read_phy_link_status(9), drm_dp_link_power_up(9), drm_dp_link_power_down(9), drm_dp_dpcd_write_payload(9), drm_dp_dpcd_clear_payload(9), drm_dp_dpcd_poll_act_handled(9), drm_dp_downstream_is_type(9), drm_dp_downstream_is_tmds(9), drm_dp_send_real_edid_checksum(9), drm_dp_read_dpcd_caps(9), drm_dp_read_downstream_info(9), drm_dp_downstream_max_tmds_clock(9), drm_dp_downstream_min_tmds_clock(9), drm_dp_downstream_max_bpc(9), drm_dp_downstream_420_passthrough(9), drm_dp_downstream_444_to_420_conversion(9), drm_dp_downstream_rgb_to_ycbcr_conversion(9), drm_dp_downstream_mode(9), drm_dp_downstream_id(9), drm_dp_downstream_debug(9), drm_dp_subconnector_type(9), drm_dp_set_subconnector_property(9), drm_dp_read_sink_count_cap(9), drm_dp_read_sink_count(9), drm_dp_remote_aux_init(9), drm_dp_aux_init(9), drm_dp_aux_register(9), drm_dp_aux_unregister(9), drm_dp_psr_setup_time(9), drm_dp_start_crc(9), drm_dp_stop_crc(9), drm_dp_read_desc(9), drm_dp_dump_lttpr_desc(9), drm_dp_dsc_sink_bpp_incr(9), drm_dp_dsc_slice_count_to_mask(9), drm_dp_dsc_sink_slice_count_mask(9), drm_dp_dsc_sink_max_slice_count(9), drm_dp_dsc_sink_line_buf_depth(9), drm_dp_dsc_sink_supported_input_bpcs(9), drm_dp_dsc_sink_max_slice_throughput(9), drm_dp_dsc_branch_max_overall_throughput(9), drm_dp_dsc_branch_max_line_width(9), drm_dp_read_lttpr_common_caps(9), drm_dp_read_lttpr_phy_caps(9), drm_dp_lttpr_count(9), drm_dp_lttpr_max_link_rate(9), drm_dp_lttpr_set_transparent_mode(9), drm_dp_lttpr_init(9), drm_dp_lttpr_max_lane_count(9), drm_dp_lttpr_voltage_swing_level_3_supported(9), drm_dp_lttpr_pre_emphasis_level_3_supported(9), drm_dp_get_phy_test_pattern(9), drm_dp_set_phy_test_pattern(9), drm_dp_as_sdp_supported(9), drm_dp_vsc_sdp_supported(9), drm_dp_vsc_sdp_pack(9), drm_dp_get_pcon_max_frl_bw(9), drm_dp_pcon_frl_prepare(9), drm_dp_pcon_is_frl_ready(9), drm_dp_pcon_frl_configure_1(9), drm_dp_pcon_frl_configure_2(9), drm_dp_pcon_reset_frl_config(9), drm_dp_pcon_frl_enable(9), drm_dp_pcon_hdmi_link_active(9), drm_dp_pcon_hdmi_link_mode(9), drm_dp_pcon_hdmi_frl_link_error_count(9), drm_dp_pcon_pps_default(9), drm_dp_pcon_pps_override_buf(9), drm_edp_backlight_set_level(9), drm_edp_backlight_enable(9), drm_edp_backlight_disable(9), drm_edp_backlight_init(9), drm_panel_dp_aux_backlight(9), drm_dp_link_symbol_cycles(9), drm_dp_bw_overhead(9), drm_dp_bw_channel_coding_efficiency(9), drm_dp_max_dprx_data_rate(9).

that's the whole friend group. every single one. iykyk 💀

side note: the dp helpers(9) double feature is genuinely in the original, we're not bugging, we're just being faithful 🫶

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okay that's the page!! main character energy from a function that literally just reads a max dot clock out of DisplayPort config bytes and hands it to you in kHz. obsessed honestly 🌈

this cutie was brought to you by the kernel docs, living under ./drivers/gpu/drm/display, dated October 2026, and yes the version stamp still calls it drm_dp_downs...max_dotclock(9) because truncation is forever. mwah 💜🎀✨