2011/2/18 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>: > Do we have any pressing need to convert AMBA stuff? I haven't heard any > reason yet to convert them to runtime PM - they don't even make any > runtime PM calls. > > Maybe Linus can comment on the PM stuff as he has SoCs with these in. > As my boards don't have any sensible PM support, I don't have any > visibility of what PM facilities would be required. Sure, basically I ACK Rabins patch and his reasoning for it. (BTW Rabin spends most of his days working on the Ux500 SoCs too.) The runtime PM we need for Ux500 is to switch off silicon core voltage first and foremost. The call I've added to switch of a core voltage regulator will need to be called when the silicon is idle. In spi/amba-pl022.c I take the most brutal approach with a recent patch: hammer off this core switch (and clock) whenever the hardware is not used. This is simple in this driver since it has no state to preserve across transfers, it is written such that the core is loaded with the appropriate state for each message. Continuing this approach we run into two problems with this and other drivers: - Hammering off/on the clock+voltage is causing delays in HW so what you want is some hysteresis (usually, wait a few us/ms then switch off) - sort of a takeoff/landing effect. - Modelling voltage domains as regulators is nice, but require us to switch on/off from process context, so we cannot do this from interrupt handlers. Both of these problems are solved by elegance if we use runtime PM, since it will provide a hysteresis timeout that can be triggered from interrupt context and call the idling hooks in process context. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
