On Thu, 24 May 2012, Ohad Ben-Cohen wrote: > Hi Guennadi, > > On Thu, May 24, 2012 at 4:07 PM, Guennadi Liakhovetski > <g.liakhovetski@xxxxxx> wrote: > > How do you know, if this is a normal sd-card slot? > > Not sure I follow the question. Sorry, I mean - you don't know what card will be plugged in, so, you cannot know, whether that specific card and its driver can be safely powered off. > But if you ask whether we can dynamically set MMC_CAP_POWER_OFF_CARD, > then we can't (with what we know today). > > This CAP is dealing with issues of specific boards which, > unfortunately, we have no way (today) to dynamically probe. > > >> No, MMC_PM_KEEP_POWER is different: it is a dynamic user decision > >> controlling whether the card should stay on while the system is > >> suspended, > > > > Isn't it both? > > Yes, you're right - we need host support to keep the card powered > while the system is suspended. > > > A complete board reset in this case will differ from the card power-off > > only in the state of the rest of the SD-card ping, e.g., the clock. So, > > additionally switching off the clock in this case should be equivalent to > > the board reset? > > Not really - consider the example I gave you, where you are required > to toggle a card reset pin after you power cycle it, but there's no > way to control that pin. In that case, only a complete board reset can > help you. > > > Given the above, wouldn't it be sufficient to test (mmc->pm_flags & > > MMC_PM_KEEP_POWER) to decide, whether the card can be suspended? > > No, > > MMC_PM_KEEP_POWER is about the ability (and desire) to keep the card > powered while the system is suspended. > > MMC_CAP_POWER_OFF_CARD is about the ability to power off the card > without killing it completely until the next board reset. Ok, I think, it's this: MMC_PM_KEEP_POWER is for system-wide suspend / resume, whereas MMC_CAP_POWER_OFF_CARD is for runtime PM. Am I right? In that case, I think, they also should function similar - wouldn't it make sense to use MMC_CAP_POWER_OFF_CARD similar to MMC_PM_KEEP_POWER - as a static capability flag (meaning, whether the board is physically able to switch power) and a dynamic flag, that, say, an SDIO function driver could set if it knows, that it cannot handle runtime power switching properly? Thanks Guennadi > These two flags really address completely different problems, despite > the similar nomenclature. > > Thanks, > Ohad. --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- 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
