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

[Adrian Hunter <adrian.hunter@intel.com>]

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).

> 
>> 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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