drm_dp_dpcd_readb(9)

💅 drm_dp_dpcd_readb — read a single byte from the DPCD ✨

okay so this is a page from the Kernel API Manual, and bestie, it's a tiny one — but it's lowkey important, so let's get into it 🫶

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✨ NAME ✨

drm_dp_dpcd_readb — read a single byte from the DPCD 🎀

(one byte. that's it. that's the whole job. queen behavior honestly 👑)

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🌸 SYNOPSIS 🌸

ssize_t drm_dp_dpcd_readb (struct drm_dp_aux *aux , unsigned int offset , u8 *valuep );

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🦋 ARGUMENTS 🦋

• aux — the DisplayPort AUX channel 💖 (this is your whole way in, the vibe conduit)
• offset — the address of the register you wanna read 🔥
• valuep — the location where the value of the register is gonna be stored ✨ (yes it's a pointer, yes it gets the byte, no we're not doing anything else with it)

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💜 DESCRIPTION 💜

So on success this bad boy returns the number of bytes transferred — which is 1 — and if things go sideways it returns a negative error code 😭 fr fr, that's the whole contract.

⚠️ real talk: in most of the cases you should be using drm_dp_dpcd_read_byte instead. like, genuinely. this one is not the main character here, it's giving "I'm the lower-level one, use the wrapper" energy 💀 so if you're wondering which to pick — it's drm_dp_dpcd_read_byte. iykyk.

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🌈 SEE ALSO 🌈

go look at the kernel file ./include/drm/display/drm_dp_helper.h and then, like, all of these icons:

• struct drm_dp_vsc_sdp(9)
• struct drm_dp_as_sdp(9)
• drm_dp_dsc_sink_supports_format(9)
• drm_edp_backlight_supported(9)
• drm_dp_is_uhbr_rate(9)
• struct drm_dp_aux_msg(9)
• struct drm_dp_aux_cec(9)
• struct drm_dp_aux(9)
• drm_dp_dpcd_read_data(9)
• drm_dp_dpcd_write_data(9)
• drm_dp_dpcd_writeb(9)
• drm_dp_dpcd_read_byte(9)
• drm_dp_dpcd_write_byte(9)
• struct drm_dp_desc(9)
• enum drm_dp_quirk(9)
• drm_dp_has_quirk(9)
• struct drm_edp_backlight_info(9)
• struct drm_dp_phy_test_params(9)

like that's a whole friend group, they all hang out together 🧚⭐

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anyway bestie, that's the whole page — short but iconic 💅 this one lives at ./include/drm/display and the version on deck is dated October 2026, so check back in if the timeline moves 🌸💖 mwah, go read your DPCD bytes responsibly 🎀