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Date: Mon, 28 Apr 2014 18:25:56 +0530 From: George Cherian <george.cherian@...com> To: Richard Cochran <richardcochran@...il.com> CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>, <linux-omap@...r.kernel.org>, <davem@...emloft.net>, <jeffrey.t.kirsher@...el.com>, <dborkman@...hat.com>, <ast@...mgrid.com>, <tklauser@...tanz.ch>, <mpa@...gutronix.de>, <bhutchings@...arflare.com>, <zonque@...il.com>, <balbi@...com>, <mugunthanvnm@...com>, <t-kristo@...com>, <mturquette@...aro.org>, <linux@....linux.org.uk>, <galak@...eaurora.org>, <ijc+devicetree@...lion.org.uk>, <mark.rutland@....com>, <pawel.moll@....com>, <robh+dt@...nel.org>, <tony@...mide.com>, <bcousson@...libre.com> Subject: Re: [PATCH 5/6] ARM: AM43xx: clk: Change the cpts ref clock source to dpll_core_m5 clk On 4/28/2014 12:40 PM, Richard Cochran wrote: > On Mon, Apr 28, 2014 at 09:40:24AM +0530, George Cherian wrote: >> cpsw_cpts_rft_clk has got the choice of 3 clocksources >> -dpll_core_m4_ck >> -dpll_core_m5_ck >> -dpll_disp_m2_ck >> >> By default dpll_core_m4_ck is selected, witn this as clock >> source the CPTS doesnot work properly. It gives clockcheck errors >> while running PTP. >> >> clockcheck: clock jumped backward or running slower than expected! > It is strange that I have never seen this error, since I have often > tested linuxptp on a beagle bone white. In beagle bone white (AM335x) CPTS has a choice of 2 clocksource -dpll_core_m5_ck -dpll_core_m4_ck and by default dpll_core_m5_ck is used. Where as in AM437x the default clocksource used is dpll_core_m4_ck . You can change the clocksource in beagle bone white by writing 1 to 0x44e00520 (By default its 0). > > Can you please explain why this clock doesn't work correctly? > >> By selecting dpll_core_m5_ck as the clocksource fixes this issue. >> In AM335x dpll_core_m5_ck is the default clocksource. > The choice of clock source in the CPTS driver originally came from > TI. It would be nice to know why that was the wrong choice. > > Thanks, > Richard -- -George -- 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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