On 30 September 2013 23:10, Guennadi Liakhovetski <g.liakhovetski@xxxxxx> wrote: > Hi Ulf > > On Mon, 30 Sep 2013, Ulf Hansson wrote: > >> This patchset is remove all code related to MMC_CLKGATE. A significant >> portion of code can then be removed from the core layer which would >> simplify maintainance. >> >> At the moment it seems like only some MIPS platforms were using >> MMC_CLKGATE, but at the same time the corresponding host drivers >> were not taking advantage of the mechanism. This made me feel confident >> in removing the feature entirely from the mmc subsystem could be done. >> >> Also do note that for host drivers that would like to implement clock >> gating as a power save operation, using runtime PM is a far easier >> way to address this. Several host drivers is already fully supporting >> this as well. >> >> Ulf Hansson (2): >> MIPS: db1235: Don't use MMC_CLKGATE >> mmc: core: Remove MMC_CLKGATE > > Do I understand correctly, that you're proposing to remove the aggressive > clock gating feature from MMC? If so, then please take into account my > NAK. At least two SD / MMC drivers, that I'm aware of, actively used and > developed on multiple platforms - sh_mmcif and tmio / sdhi implement MMC > clock gating and rely on it to save power between IO. Guennadi, thanks for your NAK, you have understood correctly what my intention is. :-) Looking into your two examples, sh_mmcif and sh_mobile_sdhci (using tmio), I realize that they use runtime PM in an awkward way. I would suggest to move parts of the clock gating from .set_ios to runtime PM callbacks instead. Obviously proper calls to pm_runtime_get|put needs to be adopted as well. pm_runtime_get|put should be used to make sure your "runtime resources" are active while I/O operations are ongoing, they aren't in those drivers as of today. So to give you some more details about why I wanted to push for a removal of MMC_CLKGATE. You have one reason above. I want host drivers that considers power save at request inactivity, to implement proper runtime PM support and to do clock gating as a part of runtime PM. There are already good references, like mmci and sdhci-* for example. MMC_CLKGATE is an old way of dealing with clock gating for power save, runtime PM is better suited and has been there now for a long time now. It is time to switch. I don't think mmc clock gating should be depending on a separate kernel config as MMC_CLKGATE, which likely is the reason to why there are no defconfig that has this option enabled. Instead RUNTIME_PM already has this implicit meaning of handling with power save at request inactivity. Finally, it is nice to remove code from a maintenance point of view. The MMC_CLKGATE code is being used in a lot of places around the core layer, since "mmc_host_clk_hold|release" needs to be called so many times. What are your thoughts on the way forward? Could we adopt fully runtime pm support for sh_mmcif sh_mobile_sdhci soon? Kind regards Ulf Hansson > > Thanks > Guennadi > >> >> Documentation/mmc/mmc-dev-attrs.txt | 10 -- >> arch/mips/configs/db1235_defconfig | 1 - >> drivers/mmc/core/Kconfig | 10 -- >> drivers/mmc/core/core.c | 116 +---------------- >> drivers/mmc/core/core.h | 3 - >> drivers/mmc/core/debugfs.c | 5 - >> drivers/mmc/core/host.c | 245 ----------------------------------- >> drivers/mmc/core/mmc.c | 6 +- >> drivers/mmc/core/sd.c | 12 +- >> drivers/mmc/core/sdio.c | 5 +- >> drivers/mmc/core/sdio_irq.c | 10 +- >> include/linux/mmc/host.h | 27 ---- >> 12 files changed, 12 insertions(+), 438 deletions(-) >> >> -- >> 1.7.9.5 >> >> -- >> 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 >> > > --- > 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
