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

[Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>]

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))).

> 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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