On Sun, Sep 21, 2014 at 03:22:41PM +0200, Cédric Tessier wrote: > OpenBSD runs impressively well on my BeagleBone, the only drawback I can > see is that the system is slowed down by poor MMC performances (due to > missing DMA support in ommmc driver I suppose ?).
Yes. The ommmc(4) driver should use DMA. Same for shdc(4). IIRC the only host controller driver that uses DMA is rtsx(4). And the generic sdmmc stack keeps cards at lowest speed settings. SD cards use 1 data line instead of possible 4 and the bus is never switched to voltage levels required for very high data rates. You will not see max performance from SD cards even with DMA. This applies to all hardware platforms. A patch for 4-data-line support was posted here: http://marc.info/?l=openbsd-tech&m=138385072607035&w=2 It wasn't committed because it breaks rtsx(4): http://marc.info/?l=openbsd-tech&m=138493960219125&w=2 I'd be very happy if this was fixed ;-)
