On 12 December 2012 12:39, Kevin Liu <keyuan.liu@xxxxxxxxx> wrote: >> From: linux-mmc-owner@xxxxxxxxxxxxxxx [mailto:linux-mmc-owner@xxxxxxxxxxxxxxx] On Behalf Of Linus Walleij >> Sent: Wednesday, December 12, 2012 2:54 PM >> To: Russell King - ARM Linux; Ulf Hansson >> Cc: linux-mmc@xxxxxxxxxxxxxxx; Chris Ball; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Ulf Hansson >> Subject: Re: [PATCH] mmc: mmci: Gate the clock in runtime suspend to save power >> >> On Tue, Dec 11, 2012 at 3:52 PM, Russell King - ARM Linux >> <linux@xxxxxxxxxxxxxxxx> wrote: >>> On Tue, Dec 11, 2012 at 03:17:54PM +0100, Ulf Hansson wrote: >>>> From: Ulf Hansson <ulf.hansson@xxxxxxxxxx> >>>> >>>> The amba bus is already performing same actions but for the apb_pclk. >>>> So here we just make sure the clock to card is gated as well to save >>>> more power. At runtime resume we will thus restore the clock again. >>> >>> And how exactly do you ensure the requirement that a certain number of >>> clocks is supplied to the card after the last command before you cut >>> the clock? >> >> Oh, that's gonna be a problem. >> >> So I can see a quite straight-forward way to do this actually: >> >> 1) Turn on MMC_CLKGATE for this driver (select from Kconfig) >> which means that the ios will be called with f=0 whenever >> the card is unused, taking into account the required number >> of clocks to the card. >> >> 2) Implement handling of f=0 from the ios in the ios callback. >> Then clk_disable(host->clk). I did a hack at this some months >> back but never got around to finish it, sorry for not doing >> that even though this clock gating was invented for the MMCI >> in the first place :-( >> >> 3) In the suspend() callback, sleep until the clock indicates >> that the card is declocked with something like: >> while (clk_is_enabled(host->clk)) { sleep(1) } >> However the clk framework does not have clk_is_enabled() >> so you'd either have to add that or use a local atomic >> variable host_clk_enabled set in (2). >> >> Should work, I think? >> > > Since we use pm runtime with delay setting to 50ms, so there is no such problem? Correct! > > Thanks > Kevin > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel Kind regards Ulf Hansson -- 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
