Seungwon, On Fri, Aug 9, 2013 at 6:35 AM, Seungwon Jeon <tgih....@samsung.com> 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. 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
