[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC V2] xen: interface: introduce pvclk interface
Hi Ian, On Thu, Jan 21, 2016 at 12:26:04PM +0000, Ian Campbell wrote: >On Thu, 2016-01-21 at 19:55 +0800, Peng Fan wrote: >> Hi Ian, >> >> On Thu, Jan 21, 2016 at 10:19:32AM +0000, Ian Campbell wrote: >> > On Thu, 2016-01-21 at 16:59 +0800, Peng Fan wrote: >> > > >> > > To platform device of ARM, hypervisor is responsible for the mapping >> > > between machine address and guest physical address, also responsible >> > > for the irq mapping. >> > > >> > > But to embedded ARM SoC, the hardware clk IP is handled in Dom0. >> > >> > Arguably Xen ought to be the one to do this, but we have determined >> > (rightly, I think) that doing so for the entirely clk tree of an SoC >> > would >> > involve importing an unmanageable amount of code into Xen[0]. >> > >> > In the meantime we defer this to Dom0. >> > >> > I wonder though if it would be possible to manage the clocks for a >> > passthrough device from the toolstack, i.e. is there a sysfs node where >> > one >> > can say "keep the clock for this device enabled (at xMhz) even though >> > you >> > think the device is unused"? >> >> I am afraid not. The linux device driver without xen can work well, >> because >> there is clk tree and "clk_get,clk_prepare,clk_set_rate" work well in the >> driver. >> I do not want to remove the clk apis usage from the device driver for >> xen, because the driver >> also serves when no xen support. The pvclk interface is mainly to let the >> clk api can work as no xen. > >Would adding a dummy fixed-clock[0] (or several of them) to the guest >passthrough DT satisfy the driver's requirements? They would be hardcoded >to whatever rate dom0 and/or the tools has decided upon (and had set in the >real h/w). If using this way, we have the assumption that DomU device driver would not change the rate of the clock driving the device. I am not sure whether this is ok for so many platform devices based ARM core. In /sys/kernel/debug/clk/...., there are clk tree info, but clk api are not exposed to userspace as far as I know, so if using sysfs interface to set a known fixed rate or enable/disable the clock, we need to expose the clk info to userspace. Jan said using hypercall in the other mail, do you have any ideas about this? Thanks, Peng. > >Ian. > >[0] Documentation/devicetree/bindings/clock/fixed-clock.txt > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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