Date:   Mon, 9 Mar 2020 10:35:31 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     Jon Hunter <jonathanh@...dia.com>,
        Bitan Biswas <bbiswas@...dia.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-block <linux-block@...r.kernel.org>,
        <lkft-triage@...ts.linaro.org>,
        open list <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        John Stultz <john.stultz@...aro.org>,
        Faiz Abbas <faiz_abbas@...com>,
        Thierry Reding <treding@...dia.com>,
        Anders Roxell <anders.roxell@...aro.org>,
        Kishon <kishon@...com>
Subject: Re: LKFT: arm x15: mmc1: cache flush error -110


On 3/6/20 3:14 AM, Ulf Hansson wrote:
> External email: Use caution opening links or attachments
>
>
> [...]
>
>>>>>>>>>>> Actually we always use R1B with CMD6 as per spec.
>>>>>>>>>> I fully agree that R1B is preferable, but it's not against the
>>>>>>>>>> spec to
>>>>>>>>>> send CMD13 to poll for busy.
>>>>>>>>>>
>>>>>>>>>> Moreover, we need to cope with the scenario when the host has
>>>>>>>>>> specified a maximum timeout that isn't sufficiently long enough for
>>>>>>>>>> the requested operation. Do you have another proposal for how to
>>>>>>>>>> manage this, but disabling MMC_RSP_BUSY?
>>>>>>>>>>
>>>>>>>>>> Let's assume you driver would get a R1B for the CMD6 (we force it),
>>>>>>>>>> then what timeout would the driver be using if we would set
>>>>>>>>>> cmd.busy_timeout to 30ms?
>>>>>>>>>>
>>>> Sorry didn't understood clearly. Are you asking with 30s timeout, whats
>>>> the data timeout counter used?
>>> Yes. It seems like it will pick the maximum, which is 11s?
>> yes
> Okay, thanks!
>
>>>> Because of above mentioned issue on our host where CMD interrupt happens
>>>> after busy state, poll for busy returns right away as not busy.
>>> I see.
>>>
>>>> So issuing CMD13 after CMD6-R1 followed by busy poll should be working.
>>>> But weird that with small delay of 1ms or debug print before CMD13 it
>>>> doesn't timeout and works all the time.
>>> I have digested the information you provided in these emails. Let me
>>> summarize it, to see if I have understood correctly.
>>>
>>> 1.
>>> Your controller can't distinguish between R1 and R1B because of a
>>> limitation in the HW. So, in both cases you need to wait for the card
>>> to stop signal busy, before the controller can give an IRQ to notify
>>> that the R1 response has been received. Correct?
>>>
>>> In this context, I am wondering if sdhci_send_command(), really
>>> conforms to these requirements. For example, depending on if the CMD6
>>> has MMC_RSP_BUSY or not, it may pick either SDHCI_CMD_RESP_SHORT or
>>> SDHCI_CMD_RESP_SHORT_BUSY.
>>>
>>> Does this work as expected for your case?
>> Design team re-verified internally and bug where HW waits for busy state
>> before IRQ is only for R1B and R1 is spec compliant.
>>
>> So, with R1, CMD complete is generated after response received.
> Okay.
>
> So, the issue we see for CMD6 with R1, is a software problem that we
> should be able to fix.
>
>> With R1B, CMD complete and xfer complete both are generated after
>> response received + device busy (max timeout of 11s)
>> DATA timeout interrupt will be asserted incase if HW busy detection fails.
>>
>> With R1B we may see DATA Timeout if operation takes more than max busy
>> timeout of 11s.
> Okay, I see.
>
>>> 2.
>>> Assuming my interpretation of the above is somewhat correct. Then you
>>> always need to set a busy timeout for R1/R1B responses in the
>>> controller. The maximum timeout seems to be 11s long. Obviously, this
>>> isn't enough for all cases, such as cache flushing and erase, for
>>> example. So, what can we do to support a longer timeouts than 11s?
>>> Would it be possible to disable the HW timeout, if the requested
>>> timeout is longer than 11s and use a SW timeout instead?
>>>
>>> Kind regards
>>> Uffe
>> For erase long operations we have register bit to enable for infinite
>> busy wait mode where host controller would be monitoring until card is busy.
> Alright, that sounds great!
>
>> But so far for emmc devices we used on our platforms, we haven't seen
>> cache flush taking more than 11s.
> I understand that 11s is probably fine to use, for most cases.
>
> However, it's not spec compliant, as for some operations there are
> simply no timeout specified. BKOPS, cache flush, sanitize are cases
> like this - and then 11s is definitely not sufficient.
>
>> Will get back on possibility of disabling HW timeout and using SW timeout..
> Thanks!
>
> I would like to get the regression fixed asap, but I also would like
> to avoid reverting patches, unless really necessary. May I propose the
> following two options.
>
> 1. Find out why polling with ->card_busy() or CMD13, for a CMD6 with
> an R1 response doesn't work - and then fix that behaviour.
>
> 2. Set the mmc->max_busy_timeout to zero for sdhci-tegra, which makes
> the core to always use R1B for CMD6 (and erase). This also means that
> when the cmd->busy_timeout becomes longer than 11s, sdhci-tegra must
> disable the HW busy timeout and just wait "forever".
>
> If you decide for 2, you can add the software timeout support on top,
> but make that can be considered as a next step of an improvement,
> rather than needed as fix. Note that, I believe there are some support
> for software timeout already in the sdhci core, maybe you need to
> tweak it a bit for your case, I don't know.
>
> Kind regards
> Uffe

Hi Uffe

Will go with 2nd option and will send patches out when ready.

BTW, Tegra host also supports SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK for 
data timeout based on host clock when using finite mode (HW busy 
detection based on DATA TIMEOUT count value when cmd operation timeout 
is < 11s for tegra host).

So, looks like we cant set host max_busy_timeout to 0 for Tegra host to 
force R1B during SWITCH and SLEEP_AWAKE.

So, was thinking to introduce host capability MMC_CAP2_LONG_WAIT_HW_BUSY 
which can be used for hosts supporting long or infinite HW busy wait 
detection and will update mmc and mmc_ops drivers to not allow convert 
R1B to R1B for hosts with this capability during SLEEP_AWAKE and SWITCH.

Thanks

Sowjanya

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