Hi. On 08/26/2014 12:20 AM, Doug Anderson wrote: > Ulf, > > On Mon, Aug 25, 2014 at 1:13 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> 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 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. > > >>>> 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 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 > -- 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
