Date:   Tue, 10 Mar 2020 09:59:10 -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 3/10/20 2:46 AM, Ulf Hansson wrote:
> External email: Use caution opening links or attachments
>
>
> On Mon, 9 Mar 2020 at 18:33, Sowjanya Komatineni <skomatineni@...dia.com> wrote:
>>
>> 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.
> Okay, good.
>
>> 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.
> That seems reasonable, it becomes probably both easier and clearer by
> adding a new host cap.
>
> In any case, let me help out and cook a patch for this for the core
> part (I leave the sdhci change to you). It may be a bit tricky,
> especially since I have currently queued a bunch of new changes for
> v5.7, that enables more users of mmc_poll_for_busy() in the core.
> Maybe I need to temporarily drop them, so we can fix these problems
> first. I will check.
>
> Probably, I would also name the cap MMC_CAP_HW_NEED_RSP_BUSY, as that
> seems to be describing the common problem we have for sdhci
> omap/tegra.
>
> Finally, it seems like MMC_CAP_WAIT_WHILE_BUSY should be set for
> sdhci- tegra, so while at it, perhaps you can cook a patch for that as
> well.
>
> Kind regards
> Uffe

OK, I sent v1 yesterday. Please ignore them then.

Will send out patches only for HW busy wait modes program based on cmd 
timeout and WAIT_WHILE_BUSY enabled.

Thanks

Sowjanya

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