Re: [RFC PATCH 0/4] mmc: core: Provide CMD5 awake and partial_init support

From: Ritesh Harjani
Date: Mon Feb 20 2017 - 08:04:41 EST

Hi Ulf,

On 2/20/2017 5:09 PM, Ulf Hansson wrote:
On 20 February 2017 at 09:03, Ritesh Harjani <riteshh@xxxxxxxxxxxxxx> wrote:
As per JEDEC spec - CMD5 can be used to awake from sleep mode for emmc.
This patch series provide CMD5(awake) + mmc_partial_init support to resume
mmc card device. This is mainly to reduce the resume time.

I assume with "resume time" you don't mean "system PM resume time"?
I meant mmc_runtime_resume time which will be accounted only in MMC card run-time resume now.

The current approach we have for MMC is to postpone system PM resume
of the card until it's actually needed, thus via runtime PM instead.
Then the time it takes to re-initialize the eMMC don't affect the
system PM resume time at all.

Therefore I am wondering about how big of a problem this really is. Is
there a specific use case you are optimizing for?
In general MMC card resume time will be optimized.

This was tested on db410c (emmc with HS200 mode) and MS8996 (emmc with HS400ES)
based internal board. This patch reduced the resume time by ~50% on msm8996
and ~11% on db410c.
Sorry, I did not enable MMC_CAP_WAIT_WHILE_BUSY on db410c. That's why we see 11% improvement only. After I enabled this cap, I see ~47% improvement in mmc_runtime_resume on db410c.

The improved behaviour in percentage is very interesting, but I would
also like to see real numbers.

1. ~110ms without the patch on db410c (with MMC_CAP_WAIT_WHILE_BUSY)

2. ~97ms with the patch on db410c (w/o enabling MMC_CAP_WAIT_WHILE_BUSY)

3. ~58ms with the patch (with MMC_CAP_WAIT_WHILE_BUSY capability).= ~47%

1. ~142ms without the patch on msm8996 (with MMC_CAP_WAIT_WHILE_BUSY)

2. ~50ms with the patch on msm8996. (with MMC_CAP_WAIT_WHILE_BUSY)= ~60%

Moreover, I would like to know what kind of mechanism the
corresponding host drivers/controllers are using for card busy
These controllers have MMC_CAP_WAIT_WHILE_BUSY capability enabled.

I have tested with below caps.

diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
index 10cdc84..2da9c4e 100644
--- a/drivers/mmc/host/sdhci-msm.c
+++ b/drivers/mmc/host/sdhci-msm.c
@@ -1283,6 +1283,9 @@ static int sdhci_msm_probe(struct platform_device *pdev)

host->mmc_host_ops.execute_tuning = sdhci_msm_execute_tuning;
+ host->mmc->caps |= MMC_CAP_WAIT_WHILE_BUSY;
+ host->mmc->caps |= MMC_CAP_AGGRESSIVE_PM;
+ host->mmc->caps2 |= MMC_CAP2_SLEEP_AWAKE;
ret = sdhci_add_host(host);
if (ret)
goto pm_runtime_disable;

As of now this patch series provides a caps (MMC_CAP2_SLEEP_AWAKE) to enable this feature.
Since there is no dependency on host platform for this, we can enable this feature by
default as well. Thoughts?

I will look into the series in more detail, however we must not add a
Sure, please let me know your feedback.

corresponding DT binding for this as this isn't a HW configuration. I
guess what you need to know is that VCCQ stays powered on when the
card is a sleep, else waking up with CMD5 won't work

The current main concern I can think of, is whether the added
complexity to the wakeup path can be justified for the improved
This may not be very complex actually.

Ritesh Harjani (4):
Documentation: mmc: add mmc-sleep-awake
mmc: core: add mmc-sleep-awake caps
mmc: mmc: add support for CMD5 awake
mmc: core: Implement mmc_partial_init during resume

Documentation/devicetree/bindings/mmc/mmc.txt | 2 +
drivers/mmc/core/core.c | 13 +++
drivers/mmc/core/core.h | 1 +
drivers/mmc/core/host.c | 2 +
drivers/mmc/core/mmc.c | 160 ++++++++++++++++++++++++--
include/linux/mmc/card.h | 3 +
include/linux/mmc/host.h | 2 +
7 files changed, 176 insertions(+), 7 deletions(-)

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Kind regards

Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project