> 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? Thanks Kevin -- 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
