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

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

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.

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>
> 
>