On 08/25/2014 05:13 PM, Ulf Hansson wrote: > On 22 August 2014 20:27, Sonny Rao <sonnyrao@xxxxxxxxxxxx> wrote: >> On Fri, Aug 22, 2014 at 8:31 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: >>> On 22 August 2014 15:47, Yuvaraj Kumar C D <yuvaraj.cd@xxxxxxxxx> wrote: >>>> 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 didn't know that use CD# line for card detect. And if CD# voltage rails and I/O voltage rail are same voltage, it doesn't make sense. Which card is used with same voltages? (eMMC? SD? SDIO?) Well, I have checked Exynos5250 and 5420, but it looks like not same rails. >>> >>> I am not sure I follow here. >>> >>> Is the card detect mechanism handled internally by the dw_mmc controller? >> >> Yes What card detect mechanism? > > 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!? > >> >>> >>> 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. >> >>>> >>>> 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 agreed with Ulf's opinion. Best Regards, Jaehoon Chung > > Kind regards > Uffe > -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
