On 27 August 2014 13:17, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > Hi Doug, > > [snip] > >>>>> 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. >>>> >>>> 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. >>> >>> I am not sure I follow to understand the problem. All I am saying is: >>> From your ->set_ios() when you get MMC_POWER_UP, enable vcc and vccq. >>> From your ->set_ios() when you get MMC_POWER_OFF, disable vccq and vcc. >>> >>> The rest is taken care of from mmc core, when trying to initialize the card. >> >> We must not be on the same page, so I'll put all my assumptions in >> super detail and we can see what's different... >> >> >> So if I have "MMC_CAP_NEEDS_POLL" set, the MMC core will poll things, >> right? ...and you are suggesting that I could solve my vqmmc vs. card >> detect problem by using MMC_CAP_NEEDS_POLL, right? > > Yes. > >> >> >> Let's think about the case when no card is inserted. When no card is >> inserted the core will call set_ios() with MMC_POWER_OFF, right? >> >> ...and we want that to turn off vmmc. >> ...and if we turn off vmmc, we should turn off vqmmc. > > Correct. At MMC_POWER_OFF, all host drivers shall turn off all the > possible powers that goes to the card. I am just telling this to make > sure, we don't think this is a dw_mmc specific thing. > >> >> Now we've got vmmc off and vqmmc off and on this board we can't read >> the card detect line, right? > > Got it. :-) > >> >> 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 the are when vccq is turned off, your ->get_cd() callback need /s /the /case > to return 0. That will allow mmc_rescan() to continue it's /s /return 0 /return 1 > initialization sequence and do mmc_power_up(). > >> >> >> ...so with that context, I'll ask my questoin again: >> >> Are you suggesting that we should flip the voltage of vqmmc (and thus >> vmmc to prevent damaging the card) during polling? That seems ugly. > > Nope. > > 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
