Hi, On Thu, Aug 28, 2014 at 10:50 AM, Sonny Rao <sonnyrao@xxxxxxxxxxxx> wrote: > On Thu, Aug 28, 2014 at 8:50 AM, Doug Anderson <dianders@xxxxxxxxxx> wrote: >> Ulf, >> >> On Thu, Aug 28, 2014 at 12:25 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: >>> On 27 August 2014 17:52, Doug Anderson <dianders@xxxxxxxxxx> wrote: >>>> Ulf, >>>> >>>> On Wed, Aug 27, 2014 at 4:17 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: >>>>>> Now, we've got MMC_CAP_NEEDS_POLL, so dw_mmc will periodically be >>>>>> called to check the card detect line, but with vmmc and vqmmc off. It >>>>>> will be unable to return a sensible value without actually turning on >>>>>> vmmc and vqmmc. >>>>> >>>>> Currently MMC_CAP_NEEDS_POLL mean the mmc rescan work will reschedule >>>>> itself with HZ interval. This to check for card insert/removal. >>>>> >>>>> Now, mmc_rescan() will, if present, invoke host's ->get_cd() callback >>>>> to check whether it's worth to continue initialization sequence or if >>>>> it should re-schedule itself again. >>>>> >>>>> If your host driver can distinguish whether a card is inserted, which >>>>> in this case are when vccq is turned off, your ->get_cd() callback need >>>>> to return 1. That will allow mmc_rescan() to continue it's >>>>> initialization sequence and do mmc_power_up(). >>>> >>>> As per my other email, we can't tell whether a card is inserted when >>>> vqmmc is off. >>> >>> I understand. >>> >>> The solution I proposed above, is: >>> >>> 1) Enable MMC_CAP_NEEDS_POLL. >>> 2) Make ->get_cd() return 1, when you can't distinguish if the card is inserted. >>> >>> That will solve this issue and without messing up the mmc core. >> >> Ah, I see! So every 1 second, we'll do the following: >> >> 1. Call get_cd(), which returns 1. >> >> 2. MMC core will power everything up (turn on all regulators) for MMC. >> >> 3. We'll start to initialize a card. >> >> 4. We'll notice that, oops, there's no card there. >> >> 5. MMC core will shut things down again. >> >> >> That seems awfully expensive to do every second when the card detect >> line actually does work (as long as you keep power lines). Is the >> patch to separate out the concepts of "power off because no card is >> inserted" and "power off because we're power cycling the card" really >> bad enough to warrant forcing us to use the above? >> >> I'm not an EE, but cycling regulators on and off every second doesn't >> seem super ideal, but maybe they're designed for it? >> >> >> Personally, I'd be tempted to just leave the power on all the time and >> if a card somehow needs to be power cycled (because UHS negotiation >> failed?) then that card just isn't supported. This could be done in >> the dts by saying that the regulator is "always on" and no need to >> pollute any source files. > > Yeah, power cycling the regulators constantly doesn't seem like a > great idea, we can ask the EEs what they think. > > This scheme of leaving them on all the time would prevent us from > being able to actually power cycle the card, which I think is required > by the spec in case UHS negotiation fails. OK, fair enough. I guess polling is less bad than nor supporting card power cycling. ...it still feels like adding this quirk to the core isn't super ugly, but if everyone is against it... -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
