SD and eMMC devices are widely present on Linux systems and became on some products the primary storage medium. One of the key feature for storage is the speed of the bus accessing the data.
Since the introduction of the original “default” (DS) and “high speed” (HS) modes, the SD card standard has evolved by introducing new speed modes, such as SDR12, SDR25, SDR50, SDR104, etc. The same happened to the eMMC standard, with the introduction of high speed modes named DDR52, HS200, HS400, etc. The Linux kernel has obviously evolved to support these new speed modes, both in the MMC core and through the addition of new drivers.
This talk will start by introducing the SD and eMMC standards and how they work at the hardware level, with a specific focus on the new speed modes. With this hardware background in place, we will then detail how these standards are supported by Linux, see what is still missing, and what we can expect to see in the future.
Grégory Clément, Bootlin