SDHCI(4)

📦 version 15.1, in freebsd 14.5, freebsd 15.1, nixpkgs unstable

💖 NAME 💖

okay so bestie, this is the sdhci(4) page from the Kernel Interfaces Manual, and it's literally the PCI SD Host Controller bridge driver. That's the whole vibe: it bridges PCI SD host controllers so your MMC/SD cards can get their main character moment. 💅

✨ SYNOPSIS ✨

To compile this driver into the kernel, place these lines in your kernel configuration file:

device mmc
device mmcsd
device sdhci

Alternatively, to load the driver as a module at boot time, put these lines in loader.conf(5):

mmc_load="YES"
mmcsd_load="YES"
sdhci_load="YES"

🌸 DESCRIPTION 🌸

So the sdhci driver supports PCI devices with class 8 and subclass 5 according to the SD Host Controller Specification. iykyk, class 8 subclass 5 is the magic combo ✨

It supports up to six high speed 4bit MMC/SD slots per controller. Six! That's a whole friend group of slots. 🫶

The driver attaches the mmc bus to the respective slot on card insertion and detaches it on card removing. Card goes in, bus says hi; card comes out, bus says bye. 😭

🔥 HARDWARE 🔥

The sdhci driver supports the SD Host Controller Specification. When attaching via the PCI bus, the controller is automatically configured. Slay, no manual config needed there. 💅

Many SoC chips provide a SDHCI controller directly mapped to I/O memory. For those, the controller may be configured using fdt(4) or acpi(4) methods, supplied by your board's vendor. So your board vendor is the one handing over the lore. 👑

Now the honest part, bestie: unlike most other drivers that support a generic standard, sdhci requires a large number of quirks to cope with hardware bugs, proprietary registers and poorly specified power management. It's giving "high maintenance but worth it" energy. 💀

While many chipsets from Intel, Xilinx, Rockchip, Frescale, Ricoh, and TI have these entries, suboptimal performance may result when using some controllers. No cap, not every controller is eating — some are just snacking. 🙈

Quirks and custom configuration are most often required when the device is configured via fdt(4) or acpi(4). So if you're on that path, expect to get cozy with quirks. 🧚

🦋 SEE ALSO 🦋

Also: SD Specifications, Part 2, SD Host Controller, Simplified Specification. The official lore drop. 📚

👑 AUTHORS 👑

  • Alexander Motin <mav@FreeBSD.org> — the icon who wrote this. Periodt. 💜

xoxo, this page was served up by Debian on October 3, 2025 — catch you in the group chat, bestie 🫶💅

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