On Sat, August 10, 2013,Doug Anderson wrote: > Seungwon, > > On Fri, Aug 9, 2013 at 6:35 AM, Seungwon Jeon <tgih.jun@xxxxxxxxxxx> wrote: > > On Wed, August 07, 2013, Doug Anderson wrote: > >> After suspend/resume all of the dw_mmc registers are reset to > >> defaults. We restore most of them, but specifically don't setup the > >> clock registers after resume unless we've got a powered card. Things > >> still work because the core will eventually call set_ios() and we'll > >> set things up. > > > > Hmm, I didn't get the need of this call during resume. > > I think set_ios is only valid where core layer calls. > > Besides, important things is ios's parameters. > > If suspend has finished successfully, last call of set_ios() is from mmc_power_off(). > > On seeing fields of 'mmc->ios' stored last, these values aren't proper in resume phase. > > Please check mmc_power_off() function. > > In case MMC_PM_KEEP_POWER it could be kept. > > Most of my reasoning has to do with the fact that the state of the > system after suspend/resume should not be significantly different than > the state of the system before suspend/resume. If the state of the > system is different in the two cases it points out potential problems > or inefficiencies. > > To make this more concrete: > > 1. Boot up a system with no card in the SD Card slot. > 2. Note down the value of registers like CLKDIV, CLKENA, etc. > 3. Suspend / resume (S2R) > 4. Check the values of CLKDIV, CLKENA, etc. > > You will notice that they are different. This is a bad sign and can > be a source of bugs (though I don't know of any). ...or it could mean > that power draw is different (could be better, could be worse) after a > suspend/resume cycle. > > > Said another way, if the value of CLKDIV, CLKENA, etc is not important > when a card is not inserted, why do they get initialized at boot time? > > > In general, I think that the mmc core code makes the assumption that > it's up to the driver to make sure that its state is preserved across > S2R. For dw_mmc the driver doesn't do the "brute force" that some > drivers do of just saving and restoring all registers using a copy > loop. Instead, the dw_mmc driver runs code that tries to set the > state back to something reasonable. Without my patch the dw_mmc > driver doesn't run any code that restores these registers. > dw_mci_set_ios() will do so. This seems pretty associated with [1/4 patch]. (Anyway continued, ...) Basically, both CLKDIV and CLKENA will be set with the reset value of zero. This means clock is disabled. While resume of dw_mmc is completed, initial configuration registers will be set except for runtime registers. I think registers related to clock are close to runtime. Core layer knows the correct clock rate for current device mode and will actually request it by set_ios. If core layer requests set_ios no more after dw_mmc resume is completed, dw_mmc will keep the clock to be disabled. Then, dw_mmc doesn't need self call of dw_mci_set_ios. Thanks, Seungwon Jeon > > Another option would be to forcibly save/restore registers in suspend/resume. > > -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
