From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean-Jacques Hiblot Date: Fri, 14 Jun 2019 17:27:29 +0200 Subject: [U-Boot] [PATCH] mmc: Avoid HS400 mode when accessing boot partitions In-Reply-To: <84b514e9-c5ec-cf22-e2c6-1bc2d14447cf@ti.com> References: <20190531132244.29719-1-marek.vasut+renesas@gmail.com> <43c3efe1-55cf-91e3-34c3-c509d0a7207d@ti.com> <3e2e9363-bf4d-84db-867b-130c3709bbb3@gmail.com> <39df182a-dbc8-b688-fa5a-43907bffc5a3@ti.com> <722b00d2-f1d2-3382-9e6c-41d1e4aa5f20@gmail.com> <84b514e9-c5ec-cf22-e2c6-1bc2d14447cf@ti.com> Message-ID: <90fb1578-0ccb-081c-cb6c-c04473618e80@ti.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Marek, Faiz, On 11/06/2019 17:59, Faiz Abbas wrote: > Hi Marek, > > On 11/06/19 3:34 PM, Marek Vasut wrote: >> On 6/11/19 10:12 AM, Faiz Abbas wrote: >>> Peng, Marek, >>> >>> On 11/06/19 6:47 AM, Peng Fan wrote: >>>>> partitions >>>>> >>>>> 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'll pick up your patch in this release. >>>> >>> The issue that Marek is facing is not a regression, is it? Are we really >>> going to merge something that we know to be wrong just so we are >>> consistently wrong? >> First of all, you established this is "wrong" without any real backing >> except for your interpretation of the specification. I would still like >> to hear from Jean the real reason why he added this filtering in the >> first place. > I think Peng agrees with my interpretation. The backing for it being > "right" is also JJ's and your interpretation of spec. The additional > justification that I am trying to give is that there is no code to > fallback in kernel and I have observed it working in kernel with no > issues. I needed your observations (with any HS200/HS400 supporting > platform) in kernel for additional data points. > >> That said, we're in rc4 , the release is just around the corner. I would >> like to avoid big changes in the MMC subsystem , or any subsystem for >> that matter. That's for next release , and if you have a patch for next, >> please post it, I am happy to test it on the hardware I have available. > I am not saying we try to fix it before this release. All I am saying is > that we don't mask real errors (none of which are regressions) with this > "fix" that we are not even sure of. > >> Also note that this patch does not have any impact on general use case, >> the regular bulk of the eMMC can be accessed at HS200/HS400, it's just >> the boot partitions which are accessed in HS52 or lower. > Exceedingly, the general usecase is to put boot images in boot partition > and root filesystem in the user data area. In that case, the boot area > is all that will be accessed in SPL at HS52 even if > CONFIG_SPL_MMC_HS200/HS400 is enabled. > >> However, right now, the behavior is not consistent between HS200 and >> HS400 modes, and I would very much like to have it consistent in the >> upcoming release. > I don't think consistency is a big enough reason to make this change. If > my interpretation is correct, you would be masking real issues for > everyone with this change and any platforms which enable HS400/HS200 > will be blissfully unaware that they are not accessing data at the > required speed. If things are failing for others, we can get their > datapoints in kernel as well. > > Having said that, if the maintainer still wants to pull this fix as is, > I would at least change the commit message to reflect our uncertainty > here so people are not mislead by this patch. > >>> Marek, I understand you do not want to debug this right now but this >>> patch will 1) Mislead people into thinking that we know what we are >>> doing (two patches went in with pretty confident patch descriptions) and >>> 2) Mask issues for people who could take the time to help debug this. >> Wrong, I want to debug this, I just don't want to do big changes in the >> upcoming release this late in the release cycle. But if you propose a >> patch for next, I am happy to test it on the hardware I have available. >> Can you send such a patch ? >> > Agreed on the no big changes this release. Hopefully we can also agree > on not having *this* change in the release either. I do not have a fix > yet but plan to look into this next week. Have you tried to use the boot partitions with HS200 lately ? I'm running a test on a DRA76 and haven't seen any issue. I wonder why it didn't work properly when I tested it back then. I also rand the same test with Linux and checked that the clock was also at 192 MHz test context: The boot partition (8MB) is accessed in HS200 mode (real freq is measured at 192 MHz with a scope) The data is fresh random data The test command is: setenv test_boot_part 'random 0x81000000 0x800000; mmc write 81000000 0 0x4000; mmc read 82000000 0 0x4000; cmp.b 81000000 82000000 0x800000' ; while run test_boot_part ; do echo -------------; done I'll post the patch for the 'random' command. If we could get this tested OK on most of the platforms that support HS200, I suggest that we remove this limitation. JJ > > Thanks, > Faiz > > >