On Tue, 2025-09-02 at 18:39 +0200, Jan Kiszka wrote: > > > I expect us to be safe and able to deal with non-pow2 regions if we use > > > QEMUSGList from the "system/dma.h" API. But this is a rework nobody had > > > time to do so far. > > > > We have to tell two things apart: partitions sizes on the one side and > > backing storage sizes. The partitions sizes are (to my reading) clearly > > defined in the spec, and the user partition (alone!) has to be power of > > 2. The boot and RPMB partitions are multiples of 128K. The sum of them > > all is nowhere limited to power of 2 or even only multiples of 128K. > > > > Re-reading the part of the device capacity, the rules are more complex: > - power of two up to 2 GB > - multiple of 512 bytes beyond that > > So that power-of-two enforcement was and still is likely too strict. > > But I still see no indication, neither in the existing eMMC code of QEMU > nor the spec, that the boot and RPMB partition sizes are included in that.
Correct. Non-power-of-two sizes are very common for real eMMCs. Taking a random one from our lab: [ 1.220588] mmcblk1: mmc1:0001 S0J56X 14.8 GiB [ 1.228055] mmcblk1: p1 p2 p3 p4 [ 1.230375] mmcblk1boot0: mmc1:0001 S0J56X 31.5 MiB [ 1.233651] mmcblk1boot1: mmc1:0001 S0J56X 31.5 MiB [ 1.236682] mmcblk1rpmb: mmc1:0001 S0J56X 4.00 MiB, chardev (244:0) For eMMCs using MLC NAND, you can also configure part of the user data area to be pSLC (pseudo single level cell), which changes the available capacity (after a required power cycle). Regards, Jan -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
