Seungwon and Jaehoon, On Fri, Aug 9, 2013 at 6:32 AM, Seungwon Jeon <tgih....@samsung.com> wrote: > On Wed, August 07, 2013, Doug Anderson wrote: >> The dw_mmc driver keeps a cache of the current slot->clock in order to >> avoid doing a whole lot of work every time set_ios() is called. >> However, after suspend/resume the register values are bogus so we need >> to ensure that the cached value is invalidated. > This mismatch comes only in case MMC_PM_KEEP_POWER, right?
Actually, no. I saw problems with the SD Card slot, which doesn't have MMC_KEEP_POWER. Problems showed up when no card was inserted across suspend/resume. In other words: 1. At boot time, slot is all setup and configured to 400kHz. 2. Suspend 3. Resume; clock registers are reset (by suspend/resume) and not restored since dw_mmc still thinks slot is configured for 400kHz due to host->current_speed cache. 4. Insert card. 5. No code sees any need to change the clock for detecting the card, since everyone thinks it's at 400kHz. ...but it's not. >> In many cases we got by without this since the core mmc code fiddles >> with the clock a lot. If we've got a card present we're probably >> running it at something like 50MHz and the core will temporarily >> switch us to 400kHz after resume. One case that didn't work (for me) >> is the case of having no card in the slot. The slot is initted to >> 400kHz at boot time. After suspend/resume the slot thinks it's still >> at 400kHz (due to the cache) so doesn't adjust timing. When it tries >> to send the command at probe time it just times out and gets left in a >> bad state. > I understand this change although some part of commit message (boot time, > probe time...) make me confused. Sorry to be confusing. I was trying to explain why the old code works fine in many cases. It's because the core MMC code tends to adjust the clock a lot around suspend/resume. When it does that, it works around this problem. ...but I found one case where suspend/resume would happen and the MMC core didn't adjust the clock. > I guess this change intends to update clock programming forcedly. > It looks like another version of 'dw_mci_setup_bus(slot, true)'. > Eventually, this change does same? Effectively, yes. As Jaehoon points out, that means we can actually eliminate the "force" parameter to dw_mci_setup_bus(). I will send a new version out that eliminates the "force" parameter and updates the commit message to (hopefully) be clearer. -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
