[U-Boot] [PATCH] mmc: Avoid HS400 mode when accessing boot partitions

Marek Vasut marek.vasut at gmail.com
Tue Jun 18 10:55:25 UTC 2019

On 6/18/19 7:03 AM, Peng Fan wrote:
>> Subject: Re: [U-Boot] [PATCH] mmc: Avoid HS400 mode when accessing boot
>> partitions
>> On 6/17/19 4:46 PM, Jean-Jacques Hiblot wrote:
>>> On 17/06/2019 12:34, Marek Vasut wrote:
>>>> On 6/17/19 11:09 AM, Jean-Jacques Hiblot wrote:
>>>>> On 15/06/2019 17:15, Marek Vasut wrote:
>>>>>> On 6/14/19 5:27 PM, Jean-Jacques Hiblot wrote:
>>>>>>> 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.
>>>>>> Do you think you can add a test.py test for this ? Then I can
>>>>>> continuously run this test on the boards I have available. It
>>>>>> should also propagate onto nvidia and xilinx boards, which I think
>>>>>> do HS modes too.
>>> I've worked on the python test for mmc writes today. I'll post it soon.
>>> It looks like HS200 for boot part is not working well yet, at least on
>>> our DRA7 platforms.
>> That's what I was afraid of.
>>> So IMO we should keep the limitation in place and add the limitation
>>> for
>>> HS400 and the python test in this release.
>>> Then we can start working on a real fix.
>> Sounds good, thanks!
> So we all agree to take this patch first, right?

I think so.

Best regards,
Marek Vasut

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