Re: [PATCH] mmc: sdhci: don't limit discard timeout by data line timeout

[Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>]

On 11/28/13 09:12, Adrian Hunter wrote:
> On 27/11/13 16:57, Vladimir Zapolskiy wrote:
>> On 11/27/13 10:21, Adrian Hunter wrote:
>>> On 26/11/13 18:33, Vladimir Zapolskiy wrote:
>>>> On 11/26/13 11:04, Adrian Hunter wrote:
>>>>> On 22/11/13 17:21, Vladimir Zapolskiy wrote:
>>>>>> On 22.11.2013 16:04, Adrian Hunter wrote:
>>>>>>> On 22/11/13 15:50, Vladimir Zapolskiy wrote:
>>>>>>>> On 22.11.2013 14:04, Adrian Hunter wrote:
>>>>>>>>> On 22/11/13 14:24, Vladimir Zapolskiy wrote:
>>>>>>>>>> On 22.11.2013 12:38, Adrian Hunter wrote:
>>>>>>>>>>> On 21/11/13 17:07, Vladimir Zapolskiy wrote:
>>>>>>>>>>>> JEDEC specification defines quite high erase timeout value for 300ms
>>>>>>>>>>>> multiplied by erase group number, and SD Host Controller
>>>>>>>>>>>> specification
>>>>>>>>>>>> data line timeout may be much less, e.g. 2^13 / 52MHz ~ 160us.
>>>>>>>>>>>>
>>>>>>>>>>>>>          From block layer and MMC perfromance perspective it is
>>>>>>>>>>>>> desirable
>>>>>>>>>>>>> that
>>>>>>>>>>>> millions of erase groups are discarded at once, so there is no much
>>>>>>>>>>>> sense to limit maximum erase timeout by data line timeout, if a
>>>>>>>>>>>> controller handles correctly erase operation without indication of
>>>>>>>>>>>> data line timeout.
>>>>>>>>>>>
>>>>>>>>>>> Would you explain that some more.  Do you mean that:
>>>>>>>>>>>          a) it does not have a timeout
>>>>>>>>>>
>>>>>>>>>> JEDEC defines a timeout on erase/trim operations, also in
>>>>>>>>>> drivers/mmc/core/core.c
>>>>>>>>>> there is a reasonable enough 10 minutes limitation for discard
>>>>>>>>>> operations.
>>>>>>>>>>
>>>>>>>>>>>          b) it has a timeout which is less than the timeout specified
>>>>>>>>>>> by the
>>>>>>>>>>> standard but the operation nevertheless completes
>>>>>>>>>>
>>>>>>>>>> SDHC data line timeout is enormously less than erase group timeout,
>>>>>>>>>> and
>>>>>>>>>> trivial testing shows that those two timeouts are independent,
>>>>>>>>>> probably
>>>>>>>>>> except some particular cases of controllers not known before commits
>>>>>>>>>> 58d1246db3 and e056a1b5b.
>>>>>>>>>>
>>>>>>>>>> According to the currently implemented logic, mmc_do_erase()
>>>>>>>>>> commonly is
>>>>>>>>>> instructed to discard 1-2 erase groups at maximum, however it tends
>>>>>>>>>> to be
>>>>>>>>>> capable to successfully discard millions of erase groups at once
>>>>>>>>>> ignoring
>>>>>>>>>> that SDHC data line timeout limitation.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> You seem to be trying to say that the SDHCI spec. says that the host
>>>>>>>>> controller does not timeout erase operations or uses a different
>>>>>>>>> timeout
>>>>>>>>> than the one programmed in the "Timeout Control Register".  Where is
>>>>>>>>> that is
>>>>>>>>> the SDHCI spec?
>>>>>>>>
>>>>>>>> According to the spec a host controller timeouts erase operations
>>>>>>>> like any
>>>>>>>> other R1B command.
>>>>>>>>
>>>>>>>> So in your opinion, should there be SDHCI_QUIRK_BROKEN_TIMEOUT_VAL
>>>>>>>> instead
>>>>>>>> of the new quirk?
>>>>>>>
>>>>>>> I don't understand how SDHCI_QUIRK_BROKEN_TIMEOUT_VAL would help.  It
>>>>>>> just
>>>>>>> sets the timeout to maximum but max_discard_to is the maximum timeout.
>>>>>>
>>>>>> Here I meant to do something like:
>>>>>>
>>>>>>        if (host->quirks&    SDHCI_QUIRK_BROKEN_TIMEOUT_VAL)
>>>>>>            mmc->max_discard_to = 0;
>>>>>>
>>>>>> Again I'm not sure that this applies well to all
>>>>>> SDHCI_QUIRK_BROKEN_TIMEOUT_VAL
>>>>>> controllers, therefore a new quirk might be better.
>>>>>>
>>>>>>> As I understand it you don't want to limit the discard size, either
>>>>>>> because
>>>>>>> your controller does not timeout, or because you are happy that the
>>>>>>> maximum
>>>>>>> timeout is enough for your users and their use-cases.
>>>>>>>
>>>>>>> If that is the case then the original patch just needs the quirk the
>>>>>>> other
>>>>>>> way around. i.e.
>>>>>>>
>>>>>>>         if (host->quirks2&     SDHCI_QUIRK2_NO_DISCARD_LIMIT)
>>>>>>>             mmc->max_discard_to = 0;
>>>>>>>         else
>>>>>>>             mmc->max_discard_to = (1<<     27) / host->timeout_clk;
>>>>>>
>>>>>> This suits me fine, thanks for review, and I'll resend a change based on
>>>>>> this.
>>>>>>
>>>>>> Also I'd like to pay your attention to (1<<    27) / host->timeout_clk
>>>>>> part of
>>>>>> calculation, following the spec it might be better to account the actual
>>>>>> value of Data Timeout Counter, otherwise a controller may get
>>>>>> unintentional
>>>>>> Data Timeout Error pretty soon. Please correct me, if I'm mistaken here.
>>>>>
>>>>> Not sure what you mean.  max_discard_to is the maximum timeout (in
>>>>> milliseconds) that the host controller supports.  The intent is to limit
>>>>> erase operations to ones that have a timeout that is less than or equal to
>>>>> that.
>>>>
>>>> That's clear. But it's not obvious why do you prefer (1<<   27) numerator
>>>> instead
>>>> of secure (1<<   13) or (1<<   (13 + sdhci_readl(host,
>>>> SDHCI_TIMEOUT_CONTROL))).
>>>
>>> The maximum value of "Data Timeout Counter Value" in "Timeout Control
>>> Register" is 14 and the maximum timeout is therefore (1<<   27).
>>
>> So, from this perspective I assume this is a potential theoretical maximum
>> timeout for a controller, which may be 16384 times more than the maximum
>> guaranteed timeout before getting a DAT timeout. Why is the theoretical maximum
>
> Where do you get the notion of "maximum guaranteed timeout"?  The timeout is
> what is programmed in "Data Timeout Counter Value".

And exactly this "Data Timeout Counter Value" is not used in your code to
predict controller's data line timeout.

>> supposed to be used in calculations of a guaranteed discard operation timeout
>> instead of promised DAT timeout by a controller?
>
> What is "promised DAT timeout"?

This is a timeout with respect to "Data Timeout Counter Value".

According to your words max_discard_to is the maximum timeout that the host
controller supports, but such a parameter is useless, because nobody sets
the host controller SDHCI_TIMEOUT_CONTROL register to maximum supported 
value,
so there is a probability that you greatly overestimate Data Timeout value,
and therefore block layer or other subsystem can't rely on it. Please 
correct
me here.

>>
>>>>
>>>>> Currently, the limit gets applied by the block layer before the mmc
>>>>> layer is
>>>>> involved so there is no possibility to take the actual timeout into
>>>>> account.
>>>>>     However if you have erase_group_def set, then it won't make any
>>>>> difference
>>>>> i.e. the limit will be the same.
>>>>>
>>>>>>
>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Potentially the change may break some of the SDHCs on discard of
>>>>>>>>>>>> mmc,
>>>>>>>>>>>> and for backward compatibility a new quirk is introduced, which
>>>>>>>>>>>> is NOT
>>>>>>>>>>>> set by default.
>>>>>>>>>>>
>>>>>>>>>>> It sounds to me that what you want to do is not standard so the quirk
>>>>>>>>>>> should
>>>>>>>>>>> be the other way around.
>>>>>>>>>>
>>>>>>>>>> Please take a look at commits 58d1246db3 and e056a1b5b, I'd be
>>>>>>>>>> glad, if
>>>>>>>>>> you
>>>>>>>>>> could elaborate to which "some host controllers" the quirk in my
>>>>>>>>>> definition
>>>>>>>>>> applies, I believe all other host controllers present at that time in
>>>>>>>>>> drivers/mmc/host/* are capable to discard without introduced
>>>>>>>>>> limitation.
>>>>>>>>>
>>>>>>>>> "some host controllers" == SDHCI i.e. to all of the ones you are
>>>>>>>>> applying
>>>>>>>>> the change.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Signed-off-by: Vladimir Zapolskiy<vladimir_zapolskiy@mentor.com>
>>>>>>>>>>>> Reported-by: Ed Sutter<ed.sutter@alcatel-lucent.com>
>>>>>>>>>>>> Cc: Chris Ball<cjb@laptop.org>
>>>>>>>>>>>> Cc: Adrian Hunter<adrian.hunter@intel.com>
>>>>>>>>>>>> ---
>>>>>>>>>>>>        drivers/mmc/host/sdhci.c  |    5 ++++-
>>>>>>>>>>>>        include/linux/mmc/sdhci.h |    1 +
>>>>>>>>>>>>        2 files changed, 5 insertions(+), 1 deletion(-)
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>>>>>>>>>>> index bd8a098..b1fdddb 100644
>>>>>>>>>>>> --- a/drivers/mmc/host/sdhci.c
>>>>>>>>>>>> +++ b/drivers/mmc/host/sdhci.c
>>>>>>>>>>>> @@ -2930,7 +2930,10 @@ int sdhci_add_host(struct sdhci_host *host)
>>>>>>>>>>>>            if (host->quirks&
>>>>>>>>>>>> SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK)
>>>>>>>>>>>>                host->timeout_clk = mmc->f_max / 1000;
>>>>>>>>>>>>
>>>>>>>>>>>> -    mmc->max_discard_to = (1<<       27) / host->timeout_clk;
>>>>>>>>>>>> +    if (host->quirks2&       SDHCI_QUIRK2_DATA_TIMEOUT_ON_DISCARD)
>>>>>>>>>>>> +        mmc->max_discard_to = (1<<       27) / host->timeout_clk;
>>>>>>>>>>>> +    else
>>>>>>>>>>>> +        mmc->max_discard_to = 0;
>>>>>>>>>>>>
>>>>>>>>>>>>            mmc->caps |= MMC_CAP_SDIO_IRQ | MMC_CAP_ERASE |
>>>>>>>>>>>> MMC_CAP_CMD23;
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/include/linux/mmc/sdhci.h b/include/linux/mmc/sdhci.h
>>>>>>>>>>>> index 3e781b8..e7f6bd2 100644
>>>>>>>>>>>> --- a/include/linux/mmc/sdhci.h
>>>>>>>>>>>> +++ b/include/linux/mmc/sdhci.h
>>>>>>>>>>>> @@ -98,6 +98,7 @@ struct sdhci_host {
>>>>>>>>>>>>        #define SDHCI_QUIRK2_CARD_ON_NEEDS_BUS_ON        (1<<4)
>>>>>>>>>>>>        /* Controller has a non-standard host control register */
>>>>>>>>>>>>        #define SDHCI_QUIRK2_BROKEN_HOST_CONTROL        (1<<5)
>>>>>>>>>>>> +#define SDHCI_QUIRK2_DATA_TIMEOUT_ON_DISCARD        (1<<6)
>>>>>>>>>>>>
>>>>>>>>>>>>            int irq;        /* Device IRQ */
>>>>>>>>>>>>            void __iomem *ioaddr;    /* Mapped address */
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>
>>>>>>
>>>>>
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