Re: [PATCH RFC] mmc: add an option to unlimit erase group count

Ulf Hansson
2013-12-17T13:41:30Z

On 17 December 2013 14:01, Vladimir Zapolskiy
<vladimir_zapolskiy@mentor.com> wrote:
> On 12/17/13 12:19, Ulf Hansson wrote:
>>
>> On 17 December 2013 10:46, Vladimir Zapolskiy
>> <vladimir_zapolskiy@mentor.com> wrote:
>>>
>>> This change adds an option to overcome a hardcoded calculation of
>>> maximum erase groups to be used for erase/trim/discard operations.
>>> This calculation is plainly based on JEDEC spec, which defines
>>> too high erase timeout delays in comparison to SDHC data line timeout.
>>
>>
>> Too high? Should they lye about the timeout instead? :-)
>>
>
> I think instead JEDEC should introduce a divider or something similar,
> because 300ms x 1M erase groups gives you 83 hours timeout for erase
> operation, which is insane to follow.

:-)

>
>
>>>
>>> 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. (1<< 13) / 52Mhz ~ 160ms.
>>>
>>> From perfromance perspective it is desirable that thousands 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.
>>>
>>> In addition setting of this option allows to erase/trim/discard MMC
>>> cards, for which previously it was reported that ioctl(BLKDISCARD) is
>>> not supported, because the currently implemented logic assumes that
>>> erase/trim/discard is supported only if data line timeout can be set
>>> higher than the erase timeout of one erase group.
>>>
>>> Note, it is possible to change mmc_core.limit_erase_groups after
>>> kernel load, but it will have no effect, because mmc block queue
>>> setup and timeout calculations are done only once during mmc_core
>>> initialization.
>>
>>
>> No, I don't believe this is the correct approach.
>
>
> Let's try to find the correct one.
>
>
>> The timeout you refer to, is not a data line timeout and it is not cmd
>> timeout either. The timeout is the busy signalling timeout or in other
>> words, the maximum time the card is allowed to stay busy.
>
>
> I refer to DAT0 line timeout:
>
> Data Timeout Counter Value
> This value determines the interval by which DAT line
> timeouts are detected.
>
> Data Timeout Error
> This bit is set when detecting one of following timeout conditions.
> (1) Busy timeout for R1b,R5b type

The above is an interesting feature. I assume it is intended to be
used for detecting busy signalling. The R1b response will be received
anyway, I suppose or?

I guess, the problem boils done to that there are a limitation in the
controller of how big timeout you can set. For some commands, like
ERASE you will potentially need a bigger timeout than what the
controller can support.

I think the easiest solution would be for the host to disable Data
Timeout Error (busy signalling) for certain commands, like ERASE. Then
instead rely on the mmc core layer to poll with CMD13 to make sure the
erase operation is completed.

Similar how omap_hsmmc is doing for ERASE.

On the other hand, if the controller supports busy signalling in
hardware, we should somehow give it provision to use it since it could
mean less polling of CMD13. I am thinking of combining
MMC_CAP_WAIT_WHILE_BUSY and host->ops->card_busy() in some smart way
from __mmc_switch() and from mmc_do_erase(). Not sure how yet. :-)

> (2) Busy timeout after Write CRC status
> (3) Write CRC Status timeout
> (4) Read Data timeout.

What controller are you referring to?

>
> CMD38 R1b ERASE
>
>
>
>> So I would suggest an approach which in the end will remove
>> "cmd_timeout_ms" from the mmc_cmd struct, since it should not be
>> needed. Additionally I think SDHCI is abusing it.
>>
>> Instead a timeout should be used while polling the card status
>> (CMD13), to make sure the card has completed it's operation as
>> expected, typically handled from mmc_do_erase() and __mmc_switch().
>
>
> I think currently set 10 seconds timeout is good enough and shouldn't
> be changed.

Actually it is today set to 10 minutes. I guess we could have an upper
limit, but still we need to have a better calculated time out, don't
we?

Kind regards
Ulf Hansson

>
> With best wishes,
> Vladimir
>
>
>> Kind regards
>> Ulf Hansson
>>
>>
>>>
>>> Signed-off-by: Vladimir Zapolskiy<vladimir_zapolskiy@mentor.com>
>>> Cc: Adrian Hunter<adrian.hunter@intel.com>
>>> ---
>>> drivers/mmc/core/Kconfig | 14 ++++++++++++++
>>> drivers/mmc/core/core.c | 11 +++++++++++
>>> drivers/mmc/host/sdhci.c | 14 +++++++++++---
>>> include/linux/mmc/host.h | 1 +
>>> 4 files changed, 37 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/Kconfig b/drivers/mmc/core/Kconfig
>>> index 269d072..9ecdde1 100644
>>> --- a/drivers/mmc/core/Kconfig
>>> +++ b/drivers/mmc/core/Kconfig
>>> @@ -26,3 +26,17 @@ config MMC_CLKGATE
>>> support handling this in order for it to be of any use.
>>>
>>> If unsure, say N.
>>> +
>>> +config MMC_UNLIMIT_ERASE_GROUPS
>>> + bool "Assume fast erase/trim/discard operation (EXPERIMENTAL)"
>>> + depends on EXPERIMENTAL
>>> + help
>>> + This option will disable limitation on maximum quantity of
>>> + erase groups to be erased/trimmed/discarded safely without
>>> + getting a timeout on DAT0 line. On old cards enabling of
>>> + this option may be unsafe, but modern eMMC cards are capable
>>> + to complete the operations in reasonable time regardless of
>>> + extremely overestimated timeout for the operations specified
>>> + by JEDEC standard.
>>> +
>>> + If unsure, say N.
>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>>> index 57a2b40..40db797 100644
>>> --- a/drivers/mmc/core/core.c
>>> +++ b/drivers/mmc/core/core.c
>>> @@ -81,6 +81,17 @@ MODULE_PARM_DESC(
>>> removable,
>>> "MMC/SD cards are removable and may be removed during suspend");
>>>
>>> +#ifdef MMC_UNLIMIT_ERASE_GROUPS
>>> +bool mmc_limit_erase_groups;
>>> +#else
>>> +bool mmc_limit_erase_groups = 1;
>>> +#endif
>>> +EXPORT_SYMBOL(mmc_limit_erase_groups);
>>> +module_param_named(limit_erase_groups, mmc_limit_erase_groups, bool,
>>> 0644);
>>> +MODULE_PARM_DESC(
>>> + limit_erase_groups,
>>> + "Erase group limitation is calculated from host's data line
>>> timeout");
>>> +
>>> /*
>>> * Internal function. Schedule delayed work in the MMC work queue.
>>> */
>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>> index bd8a098..541e9af 100644
>>> --- a/drivers/mmc/host/sdhci.c
>>> +++ b/drivers/mmc/host/sdhci.c
>>> @@ -736,8 +736,13 @@ static void sdhci_prepare_data(struct sdhci_host
>>> *host, struct mmc_command *cmd)
>>> WARN_ON(host->data);
>>>
>>> if (data || (cmd->flags& MMC_RSP_BUSY)) {
>>>
>>> - count = sdhci_calc_timeout(host, cmd);
>>> - sdhci_writeb(host, count, SDHCI_TIMEOUT_CONTROL);
>>> + if (cmd->opcode == MMC_ERASE&& !mmc_limit_erase_groups)
>>> {
>>>
>>> + sdhci_mask_irqs(host, SDHCI_INT_TIMEOUT);
>>> + } else {
>>> + sdhci_unmask_irqs(host, SDHCI_INT_TIMEOUT);
>>> + count = sdhci_calc_timeout(host, cmd);
>>> + sdhci_writeb(host, count, SDHCI_TIMEOUT_CONTROL);
>>> + }
>>> }
>>>
>>> if (!data)
>>> @@ -2930,7 +2935,10 @@ 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 (mmc_limit_erase_groups)
>>> + 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/host.h b/include/linux/mmc/host.h
>>> index 99f5709..7c93bb8 100644
>>> --- a/include/linux/mmc/host.h
>>> +++ b/include/linux/mmc/host.h
>>> @@ -426,6 +426,7 @@ int mmc_pm_notify(struct notifier_block
>>> *notify_block, unsigned long, void *);
>>>
>>> /* Module parameter */
>>> extern bool mmc_assume_removable;
>>> +extern bool mmc_limit_erase_groups;
>>>
>>> static inline int mmc_card_is_removable(struct mmc_host *host)
>>> {
>>> --
>>> 1.7.10.4
>>>
>>> --
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>>
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