Re: [PATCH 2/2] mmc: core: fix performance regression initializing MMC host controllers

Ulf Hansson
2013-04-05T09:49:34Z

On 5 April 2013 09:26, Adrian Hunter <adrian.hunter@intel.com> wrote:
> On 05/04/13 00:02, Ulf Hansson wrote:
>> On 4 April 2013 15:41, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>> Commit fa5501890d8974301042e0202d342a6cbe8609f4 introduced a performance
>>> regression by adding mmc_power_up() to mmc_start_host(). mmc_power_up()
>>> is not necessary to host controller initialization, it is part of card
>>> initialization and is performed anyway asynchronously.
>>
>> This commit message is a bit miss-leading. In eMMC case, when the host
>> driver has no possibility of power cycle the VCCQ power supply but
>> only the VCC, this is the only proper way to prevent violation of the
>> eMMC spec.
>
> But that is not true. The host controller driver can manage the voltages.
> The patch is a workaround for the regulator_init_complete late initcall.

In my view, the host driver is not responsible for implementing the
mmc/sd/sdio protocol as such, that is the core layer responsibility.
Moreover I don't think you should consider this as a workaround, it is
a proper fix to make sure we follow eMMC spec.

I noticed you V2 patch, but would still like some more clear
information in there and maybe mention "boot time performance" instead
of just "performance".

Kind regards
Ulf Hansson

>
> I deliberately did not paraphrase the original commit so that people who
> wanted to know would have to look at it for themselves. I really cannot add
> things to my commit message that do not make sense to me.
>
>>
>>>From SD-card point of view, it is not needed, so this can be optimized
>> to be done as before in an asynchronous mode.
>>
>>>
>>> This patch allows a driver to leave the power up in asynchronous code
>>> (as it was before).
>>>
>>> On my current target platform this reduces driver initialization from:
>>>
>>> [ 1.313220] initcall sdhci_acpi_driver_init+0x0/0x12 returned 0 after 102008 usecs
>>>
>>> to this:
>>>
>>> [ 1.217209] initcall sdhci_acpi_driver_init+0x0/0x12 returned 0 after 8331 usecs
>>>
>>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>>> ---
>>> drivers/mmc/core/core.c | 3 ++-
>>> drivers/mmc/host/sdhci-acpi.c | 2 ++
>>> include/linux/mmc/host.h | 1 +
>>> 3 files changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>>> index 3bf1c46..c1893c9 100644
>>> --- a/drivers/mmc/core/core.c
>>> +++ b/drivers/mmc/core/core.c
>>> @@ -2416,7 +2416,8 @@ void mmc_start_host(struct mmc_host *host)
>>> {
>>> host->f_init = max(freqs[0], host->f_min);
>>> host->rescan_disable = 0;
>>> - mmc_power_up(host);
>>> + if (!(host->caps2 & MMC_CAP2_NO_PRESCAN_POWERUP))
>>> + mmc_power_up(host);
>>> mmc_detect_change(host, 0);
>>> }
>>>
>>> diff --git a/drivers/mmc/host/sdhci-acpi.c b/drivers/mmc/host/sdhci-acpi.c
>>> index 2592ddd..7bcf74b 100644
>>> --- a/drivers/mmc/host/sdhci-acpi.c
>>> +++ b/drivers/mmc/host/sdhci-acpi.c
>>> @@ -195,6 +195,8 @@ static int sdhci_acpi_probe(struct platform_device *pdev)
>>> host->mmc->pm_caps |= c->slot->pm_caps;
>>> }
>>>
>>> + host->mmc->caps2 |= MMC_CAP2_NO_PRESCAN_POWERUP;
>>> +
>>> err = sdhci_add_host(host);
>>> if (err)
>>> goto err_free;
>>> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
>>> index 17d7148..8873e83 100644
>>> --- a/include/linux/mmc/host.h
>>> +++ b/include/linux/mmc/host.h
>>> @@ -280,6 +280,7 @@ struct mmc_host {
>>> #define MMC_CAP2_PACKED_WR (1 << 13) /* Allow packed write */
>>> #define MMC_CAP2_PACKED_CMD (MMC_CAP2_PACKED_RD | \
>>> MMC_CAP2_PACKED_WR)
>>> +#define MMC_CAP2_NO_PRESCAN_POWERUP (1 << 14) /* Don't power up before scan */
>>>
>>> mmc_pm_flag_t pm_caps; /* supported pm features */
>>>
>>> --
>>> 1.7.11.7
>>>
>>
>>
>> Some update to the commit msg, then I am happy.
>>
>> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
>>
>>
>