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

Ulf Hansson
2013-12-17T21:41:55Z

On 17 December 2013 15:06, Vladimir Zapolskiy <vz@mleia.com> wrote:
> On 12/17/13 14:41, Ulf Hansson wrote:
>>
>> 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 suppose if Data Timeout Error Status Enable bit in Error Interrupt Status
> Enable Register (Offset 036h) is not set, there will be no busy signaling
> detection.
>
>
>> 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.
>
>
> Right, see the code, that's exactly what I propose.

Sorry, I should obviously had a closer look, but kind of stopped when
I realize that you wanted to invent a Kconfig option and a module
parameter to support this. That seems like too heavy.

omap_hsmmc supports MMC_CAP_WAIT_WHILE_BUSY, sdhci does not. Still
sdhci seems to support some kind of busy detection, could you
elaborate why MMC_CAP_WAIT_WHILE_BUSY isn't set for sdhci?

Finally, I would prefer a solution which is more mmc core layer
centric. The problem is not only related to ERASE, there are other
SWITCH operations like sanitize, cache ctrl, bkops, etc that need big
time out values.

For host drivers that supports, MMC_CAP_WAIT_WHILE_BUSY, I think it
would make sense to have a common way for the mmc core layer to notify
them about the wanted time out. That will give them provision to set
the wanted time out value or to make it indefinite, depending on what
they can support.

So maybe, "cmd_timeout_ms" in the mmc_cmd struct actually can be used
for this!? Maybe that was even the intent when adding it a few years
ago. :-)

Kind regards
Uffe

>
>
>> 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?
>
>
> This is from SD Specifications Part A2 SD Host Controller Simplified
> Specification Version 3.00 February 25, 2011.
>
>
>>>
>>> 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.
>
>
> Right, sorry for confusion.
>
>
>> I guess we could have an upper limit, but still we need to have
>> a better calculated time out, don't we?
>
>
> Best of all is to have a reasonable timeout (10 minutes is reasonable
> enough?), but my point is that its definition should be driven by user
> expectation, and it should not be based on Data Timeout Counter Value
> and/or TRIM_MULT, ERASE_TIMEOUT_MULT etc.
>
> I see an alternative, in case when e.g. 1 to 100 erase groups are
> selected by a user, let's follow JEDEC timeout (but disable Data
> Timeout Error interrupt), otherwise limit an operation by 10 minutes.
>
>
> 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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