On Thu, May 03, 2012 at 06:21:27PM +0000, Bedia, Vaibhav wrote: > On Thu, May 03, 2012 at 21:39:18, Mark A. Greer wrote: > > On Thu, May 03, 2012 at 10:44:44AM +0000, Bedia, Vaibhav wrote: > > > On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote: > > > > From: "Mark A. Greer" <mgreer@xxxxxxxxxxxxxxx> > > > > > > > > The davinci EMAC driver has been incorporated into the am35x > > > > family of SoC's which is OMAP-based. The incorporation is > > > > incomplete in that the EMAC cannot unblock the [ARM] core if > > > > its blocked on a 'wfi' instruction. This is an issue with > > > > the cpu_idle code because it has the core execute a 'wfi' > > > > instruction. > > > > > > > > To work around this issue, add platform data callbacks which > > > > are called at the beginning of the open routine and at the > > > > end of the stop routine of the davinci_emac driver. The > > > > callbacks allow the platform code to issue disable_hlt() and > > > > enable_hlt() calls appropriately. Calling disable_hlt() > > > > prevents cpu_idle from issuing the 'wfi' instruction. > > > > > > > > It is not sufficient to simply call disable_hlt() when > > > > there is an EMAC present because it could be present but > > > > not actually used in which case, we do want the 'wfi' to > > > > be executed. > > > > > > > > > > Are you trying to say that if ARM executes _just_ wfi and _absolutely > > > nothing else_ is done in the OMAP PM code, EMAC stops working? > > > > No, I'm saying the EMAC can't wake the core from the wfi so if nothing > > else happens in the system, its effectively hung. If something else > > does happen in the system (e.g., a timer expires), the the system is > > extremely slow because because its only waking up when a timer (or > > something else wakes it up--but not net traffic). This is very apparent > > when using an nfs-mounted rootfs. It doesn't hang but its extremely > > slow because occasionally something else wakes up the core but it > > spends most of its time stuck in the wfi when it should be handling > > net/nfs traffic. > > > > So, if I understood this correctly, it's effectively like blocking a low power > state transition (here wfi execution) when EMAC is active? Assuming "it" is my patch, correct. Mark -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
