Linux 5.14 Bringing SD Cache Ctrl Support, Other SD Card Support Improvements

Written by Michael Larabel in Linux Storage on 2 July 2021 at 01:00 PM EDT. 2 Comments
The MMC/MEMSTICK updates for Linux 5.14 bring more work on bettering the kernel's Secure Digital card support.

Sent in earlier this week was the MMC/MEMSTICK updates for Linux 5.14 and from those various changes catching our eye were a number of Secure Digital (SD) related improvements and supporting more functionality on that front. It was only last year that SD Express support got ironed out and some other SD features have lagged behind in the past while now the mainline kernel is working in the direction of catching up.

- Cache control "Cache Ctrl" support for SD 6.x cards and later. The SD specification allows for an optional internal cache on the SD card for bettering the performance, but that cache needs to be controlled by the host. In particular, the host ends up needing to enable it and manage the flushing of that cache. With Linux 5.14 this Cache Ctrl support is in place for SD cards offering such an internal cache.

- Linux 5.14 also now supports power off notifications for SD cards. For system suspend, run-time suspend, or system shutdown, there is now a "graceful power-off sequence" applied via making use of the SD Power Off Notification functionality since the SD 4.x specification.

- Linux 5.14 also now supports the reading and writing of SD function extension registers.

- Enabling the UHS-I voltage switch for SDSC. In turn this should make it so such SDSC cards aren't throttled to 25MB/s.

More details on the MMC/MEMSTICK changes for Linux 5.14 via this pull request that already has landed in mainline.
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