On 6/11/19 5:25 PM, Jean-Jacques Hiblot wrote: > + Jaehoon > > > Hi Marek, > > On 10/06/2019 13:33, Marek Vasut wrote: >> On 6/10/19 7:59 AM, Peng Fan wrote: >>>> 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. >> So are we gonna leave this inconsistency in for current release or >> what's it gonna be ? Like I said, we're in rc3, it's fine to do bigger >> changes in next release, but we should at least fix this in current >> release. >> >> I would also like to hear from Jean why he originally introduced this >> for HS200 mode. > > Well I didn't look into the specs when working on this part. > > I introduced it because of Jaehoon's remark on this thread: > https://lists.denx.de/pipermail/u-boot/2017-January/278672.html
Aha > Maybe Jaehoon can help us here understand why it is needed. I'm afraid Jaehoon was MIA for a while :( -- Best regards, Marek Vasut _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
