Hi.

On 08/26/2014 12:20 AM, Doug Anderson wrote:

Ulf,

On Mon, Aug 25, 2014 at 1:13 AM, Ulf Hansson [off-list ref] wrote:

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On 22 August 2014 20:27, Sonny Rao [off-list ref] wrote:

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On Fri, Aug 22, 2014 at 8:31 AM, Ulf Hansson [off-list ref] wrote:

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On 22 August 2014 15:47, Yuvaraj Kumar C D [off-list ref] wrote:

quoted

Exynos 5250 and 5420 based boards uses built-in CD# line for card
detection.But unfortunately CD# line is on the same voltage rails
as of I/O voltage rails. When we cut off vqmmc,the consequent card
detection will break in these boards.

I am not sure I follow here.

Is the card detect mechanism handled internally by the dw_mmc controller?

Yes

Just out of curiosity.

Do you know how the power to the actual dw_mmc controller is handled?
I expect it to be SoC specific and I am guessing power domain
regulators may be involved!?

You can likely read the dw_mmc registers when vqmmc is off.  Is that
what you're asking?  Certainly if vqmmc is not powered then the lines
themselves will be useless, won't they?  The "vqmmc" supply goes to
the "VDDQ_MMC2" pin on 5420.  In my 5420 user manual, I see that
"clk", "cmd", "cd", "datN", "wp" and "biuvr" pins are all in this same
voltage (VDDQ_MMC2) domain.  Can you really read a pin without
powering that part of the SoC?

It's not correct.
At TRM, described as same voltage domain. But CD-pin is used with "always-on" power.
In circuit, CD# pin is disconnected.

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I thought HW engineers long time ago realized that this should be done
separately on a GPIO line to be able to save power while waiting for a
card to be inserted. But that's not case then?

At least in my limited experience, this seems to be common among SoC
vendors who are using dw_mmc, as we've seen this elsewhere as well and
after seeing it here we know that we need to ignore the CD pin that's
routed to dw_mmc and use a separately powered GPIO on the board, but
still there are probably many SoCs/boards which are doing it this way.

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These hosts (obviously) need to keep vqmmc (and thus vmmc) on all the
time, even when the mmc core tells them to power off. However, one
problem is that these cards won't properly handle mmc_power_cycle().
That's needed to handle error cases when trying to switch voltages
(see 0797e5f mmc:core: Fixup signal voltage switch).

This patch adds a new MMC_POWER_OFF_HARD mode when it's doing a power
cycle.  This mode differs from the normal MMC_POWER_OFF mode in that
the mmc core will promise to power the slot back on before it expects
the host to detect card insertion or removal.

This patch is based off of one that Doug wrote (sent privately to
Yuvaraj) which just modifies the MMC core, and should be split into
two patches.
One that modifies the mmc core and one that implements this in dw_mmc.

I looked at the mmc core parts, it seems like the wrong approach.

I think you shall be able use MMC_CAP_NEEDS_POLL, to handle this
broken card detect mechanism. We even have a DT binding for that,
"broken-cd".

I don't think this is possible, but let me explain why I think so and
you can correct me.

Exynos series is using the external gpio-cd concept. So it need not to use MMC_CAP_NEEDS_POLL.
Can use the slot-gpio API. In my exynos5 board, it's working fine with the slot-gpio API.

Best Regards,
Jaehoon Chung

The voltage domain of the "card detect" pin on the SoC is vqmmc,
right?  That means that you won't be able to read the pin without
turning on vqmmc.  Even if you could read the pin without turning on
vqmmc, the pullup on this line is connected to vqmmc too.  ...so if
vqmmc is off then there's no pulup and you can't use card detect.

Are you suggesting that we should flip the voltage of vqmmc (and thus
vmmc to prevent damaging the card) during polling?  That seems ugly.


One other thing to mention: we didn't find any power savings by
actually turning off vmmc and vqmmc when there was no card inserted.
There's no current running through the lines when there is no card
inserted and apparently everything is efficient enough that there was
no problem.

-Doug