On czw, 2015-01-15 at 09:20 +0100, Ulf Hansson wrote: > + Mike, Stephen (Clock maintainers) > > On 12 January 2015 at 10:23, Krzysztof Kozlowski > <k.kozlowski@xxxxxxxxxxx> wrote: > > Hi, > > > > > > I would like to hear some comments about idea of scaling MMC clock > > frequency. The basic idea is to lower the clock when device is > > completely idle or not busy enough. > > We already have host drivers that implements runtime PM support. > Typically that would mean the clock will be gated once the device > becomes runtime PM suspended. > > Why should we decrease the frequency of an already gated clock? In case of idle state you're right that clkgate would be better. But what about finding a compromise between high performance (high frequency) and energy saving for different loads on MMC? The frequency scaling could help in that case. Anyway I should prepare some more benchmarks for such conditions. Best regards, Krzysztof > I think this boils done to how DVFS transitions can be triggered from > the clock drivers, right? > > Currently the clock framework supports this through clock rate change > notifiers. Should we have clock notifiers for clk_prepare|unprepare() > as well? I do remember that someone posted patches for that a while > ago, but those were rejected. > > Mike, Stephen - comments? > > Kind regards > Uffe > > > > > The patchset adds MMC card as a devfreq device and uses simple_ondemand > > as governor. In idle this gave benefits (less energy consumed during > > idle): > > 1. Trats2 (Exynos4412): 2.6% > > 2. Rinato (Exynos3250): 1% > > > > but (especially on Rinato) it had impact on performance (probably > > because ondemand triggering a little to late). What is interesting > > manually changing the clock (without this patchset) gave slightly > > bigger benefits. Maybe the devfreq introduces noticeable overhead? > > > > > > Comments are welcomed. Maybe on other platforms this has bigger impact? > > > > Best regards, > > Krzysztof > > > > > > Krzysztof Kozlowski (3): > > mmc: Add dynamic frequency scaling > > ARM: dts: Specify MSHC realistic clocks and use frequency scaling > > ARM: dts: Use frequency scaling for MSHC > > > > Documentation/devicetree/bindings/mmc/mmc.txt | 2 + > > arch/arm/boot/dts/exynos3250-rinato.dts | 1 + > > arch/arm/boot/dts/exynos4412-trats2.dts | 4 +- > > drivers/mmc/card/block.c | 247 ++++++++++++++++++++++++++ > > drivers/mmc/core/Kconfig | 16 ++ > > drivers/mmc/core/core.h | 1 - > > drivers/mmc/core/host.c | 2 + > > include/linux/mmc/card.h | 8 + > > include/linux/mmc/host.h | 3 + > > 9 files changed, 282 insertions(+), 2 deletions(-) > > > > -- > > 1.9.1 > > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
