> Subject: Re: [U-Boot] [PATCH] mmc: Avoid HS400 mode when accessing boot > partitions > > Hi Marek, Peng, > > On 03/06/19 12:04 PM, Peng Fan wrote: > > > >> Subject: [PATCH] mmc: Avoid HS400 mode when accessing boot partitions > >> > >> According to JEDEC JESD84-B51.pdf section 6.3.3 Boot operation , > >> HS200 & HS400 mode is not supported during boot operation. The U-Boot > >> code currently only applies this restriction to HS200 mode, extend > >> this to > >> HS400 mode as well. > The spec in section 6.3.3 (according to my understanding) is talking about > "boot operation" which is a way of getting data from the the eMMC without > going through the Device identification mode (Section 6.4.4) i.e. without > sending any commands. All the host has to do is hold the command line low in > Pre-Idle mode to automatically receive data at the preconfigured frequency > and bus width. > > When U-boot is accessing the partition, it has already gone through the > Device identification mode and is in data transfer mode (i.e. it needs to send > commands for read/write to happen). In this case, we need to switch the > partition in Extended CSD to access the boot partition (Section 6.2.5). The > spec doesn't say anything about HS200 and HS400 not being supported here.
Yes, the spec does not mention this. It only mentions HS200/400 not supported during boot operation. > > Also, I don't see linux kernel switching down speed when trying to access a > boot partition (unless its being very sneaky about it). So if you are seeing > issues with accessing boot partitions at HS200/HS400 then you should > probably look at how linux code is working instead. There might be bug in U-Boot code. Regards, Peng. > > Thanks, > Faiz > _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
