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

Adrian Hunter
2013-04-05T07:21:21Z

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>
>
>