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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen/arm: Set up Versatile Express timer frequency to 24 Mhz
On 06/26/2013 11:52 AM, Tim Deegan wrote: > At 11:24 +0100 on 26 Jun (1372245863), Stefano Stabellini wrote: >> On Wed, 26 Jun 2013, Tim Deegan wrote: >>> At 09:05 +0900 on 26 Jun (1372237555), Sengul Thomas wrote: >>>>> >>>>> Timers on ARM seems a bit complex. The current issue is with arch timer >>>>> (which is also used by dom0). >>>> >>>> Just out of curiosity, what is the difference between arch timer and >>>> platform timer? >>> >>> The arch timer has its interface specified in the CPU manual and >>> required (IIRC) for any processor that supports the virt extensions. >>> The platform timers are whatever other time sources come on the SoC >>> you're running on. >>> >>> Having thought about this a bit, ISTR that the register in Julien's >>> patch doesn't control anything -- it's there to tell the arch timer's >>> users how fast that timer is going, so it ought to be set up by whatever >>> sets up the timer itself (turning on oscillators &c). >>> >>> So the right thing to do is to move that write into more board-specific >>> start-of-day code (and eventually into the boot-wrapper), and rely on >>> the bootloader/firmware to have done it in the general case. >> >> I think that you are right >> >> >>> On a real >>> TC2 is that register already correct at (xen's) boot time? >>> >>> But presumably just changing it from 100KHz to 24KHz for all vexpresses >>> is wrong because that will break things on the software models in the >>> opposite way. >> >> I think we should read CNTFRQ at boot time rather than trying to write >> it. We should be able to cope with whatever frequency has been setup by >> the firmware, right? > > Yes -- in the case where the firmware has done it, we should be reading > this register rather than writing it. Xen already reads the timer frequency in arm/time.c. > On the software VE model the code was developed on, there is no firmware > and so Xen has to set this up along with the other things that we'd > expect firmware to do. So we can move that write to the start-fo-day > board-specific asm hacks, and the actual driver code can just read it. Is it possible to start to use u-boot on the VE model? So we can remove the code which set up the timer freqency. -- Julien _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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