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

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:

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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!?

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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".

Kind regards
Uffe