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 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!? > >> >> 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". 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
