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Message-ID: <op.x6iz21fw1774gr@chall-mobl2.amr.corp.intel.com> Date: Wed, 14 Oct 2015 19:34:03 -0700 From: "Christopher Hall" <christopher.s.hall@...el.com> To: "Thomas Gleixner" <tglx@...utronix.de>, "Richard Cochran" <richardcochran@...il.com> Cc: jeffrey.t.kirsher@...el.com, hpa@...or.com, mingo@...hat.com, john.stultz@...aro.org, peterz@...radead.org, x86@...nel.org, intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kevin.b.stanton@...el.com Subject: Re: [PATCH v4 1/4] Produce system time from correlated clocksource Richard, On Tue, 13 Oct 2015 14:12:24 -0700, Richard Cochran <richardcochran@...il.com> wrote: > On Tue, Oct 13, 2015 at 09:15:51PM +0200, Thomas Gleixner wrote: > Can we at least have a explanation of how the firmware operates? How > are (ART,sys) pairs are generated, and how they are supposed to get > into the DSP? I'll give it a try. The audio controller has a set of registers almost exactly like those on the network device. The e1000e patch adds the e1000e_phc_get_ts() function. It writes a register to start the cross-timestamp process and some time later the hardware sets a bit indicating that it's finished. In the case of the network, the host polls for this bit to be set, indicating the cross-timestamp registers have valid data. In the audio DSP case, it is the DSP that's doing the polling and it can only poll once per millisecond. The transfers look like: Host -PCI (write request) -> DSP [Transaction started from host] DSP -PCI (write to initiate)-> Audio controller [Transaction started from DSP] DSP <-PCI (read to poll status)- Audio Controller [Transaction Complete from DSP perspective] DSP <-PCI (read (ART,device) pair)- Audio Controller DSP -PCI (write notification) -> Host [Transaction complete from Host perspective] Host <-PCI read (ART,device) pair- DSP I hope this is helpful. Thanks. Chris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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