From: Richard Cochran <richardcochran@gmail.com>
To: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: "David S. Miller" <davem@davemloft.net>,
netdev@vger.kernel.org, Mugunthan V N <mugunthanvnm@ti.com>,
Sekhar Nori <nsekhar@ti.com>,
linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org,
WingMan Kwok <w-kwok2@ti.com>
Subject: Re: [PATCH 7/9] net: ethernet: ti: cpts: calc mult and shift from refclk freq
Date: Wed, 14 Sep 2016 22:26:19 +0200 [thread overview]
Message-ID: <20160914202618.GC12195@netboy> (raw)
In-Reply-To: <20160914130231.3035-8-grygorii.strashko@ti.com>
On Wed, Sep 14, 2016 at 04:02:29PM +0300, Grygorii Strashko wrote:
> +static void cpts_calc_mult_shift(struct cpts *cpts)
> +{
> + u64 maxsec;
> + u32 freq;
> + u32 mult;
> + u32 shift;
> + u64 ns;
> + u64 frac;
> +
> + if (cpts->cc_mult || cpts->cc.shift)
> + return;
> +
> + freq = clk_get_rate(cpts->refclk);
> +
> + /* Calc the maximum number of seconds which we can run before
> + * wrapping around.
> + */
> + maxsec = cpts->cc.mask;
> + do_div(maxsec, freq);
> + if (!maxsec)
> + maxsec = 1;
This doesn't pass the smell test. If the max counter value is M, you
are figuring M*1/F which is the time in seconds corresponding to M.
We set M=2^32-1, and so 'freq' would have to be greater than 4 GHz in
order for 'maxsec' to be zero. Do you really expect such high
frequency input clocks?
> + else if (maxsec > 600 && cpts->cc.mask > UINT_MAX)
> + maxsec = 600;
What is this all about? cc.mask is always 2^32 - 1.
> + clocks_calc_mult_shift(&mult, &shift, freq, NSEC_PER_SEC, maxsec);
> +
> + cpts->cc_mult = mult;
> + cpts->cc.mult = mult;
In order to get good resolution on the frequency adjustment, we want
to keep 'mult' as large as possible. I don't see your code doing
this. We can rely on the watchdog reader (work queue) to prevent
overflows.
Thanks,
Richard
> + cpts->cc.shift = shift;
> + /* Check calculations and inform if not precise */
> + frac = 0;
> + ns = cyclecounter_cyc2ns(&cpts->cc, freq, cpts->cc.mask, &frac);
> +
> + dev_info(cpts->dev,
> + "CPTS: ref_clk_freq:%u calc_mult:%u calc_shift:%u error:%lld nsec/sec\n",
> + freq, cpts->cc_mult, cpts->cc.shift, (ns - NSEC_PER_SEC));
> +}
next prev parent reply other threads:[~2016-09-14 20:26 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-14 13:02 [PATCH 0/9] net: ethernet: ti: cpts: update and fixes Grygorii Strashko
2016-09-14 13:02 ` [PATCH 1/9] net: ethernet: ti: exclude cpts from build when disabled Grygorii Strashko
2016-09-14 13:02 ` [PATCH 2/9] net: ethernet: ti: cpsw: minimize direct access to struct cpts Grygorii Strashko
2016-09-14 13:02 ` [PATCH 3/9] net: ethernet: ti: cpts: rework initialization/deinitialization Grygorii Strashko
2016-09-14 13:52 ` Richard Cochran
2016-09-14 20:10 ` Grygorii Strashko
2016-09-14 20:32 ` Richard Cochran
2016-09-14 20:37 ` Grygorii Strashko
2016-09-14 20:52 ` Richard Cochran
2016-09-14 20:59 ` Grygorii Strashko
2016-09-15 8:13 ` Richard Cochran
2016-09-14 13:02 ` [PATCH 4/9] net: ethernet: ti: cpts: move dt props parsing to cpts driver Grygorii Strashko
2016-09-14 13:55 ` Richard Cochran
2016-09-14 19:45 ` Grygorii Strashko
2016-09-14 20:03 ` Richard Cochran
2016-09-14 13:02 ` [PATCH 5/9] net: ethernet: ti: cpts: add return value to tx and rx timestamp funcitons Grygorii Strashko
2016-09-14 14:00 ` Richard Cochran
2016-09-14 13:02 ` [PATCH 6/9] net: ethernet: ti: cpts: clean up event list if event pool is empty Grygorii Strashko
2016-09-14 14:14 ` Richard Cochran
2016-09-14 19:54 ` Grygorii Strashko
2016-09-14 13:02 ` [PATCH 7/9] net: ethernet: ti: cpts: calc mult and shift from refclk freq Grygorii Strashko
2016-09-14 14:22 ` Richard Cochran
2016-09-14 19:59 ` Grygorii Strashko
2016-09-14 20:26 ` Richard Cochran [this message]
2016-09-14 20:47 ` Grygorii Strashko
2016-09-14 21:03 ` Richard Cochran
2016-09-14 21:14 ` Grygorii Strashko
2016-09-15 11:58 ` Richard Cochran
2016-09-15 13:49 ` Richard Cochran
2016-09-14 13:02 ` [PATCH 8/9] net: ethernet: ti: cpts: fix overflow check period Grygorii Strashko
2016-09-14 14:25 ` Richard Cochran
2016-09-14 20:03 ` Grygorii Strashko
2016-09-14 20:08 ` Richard Cochran
2016-09-14 20:23 ` Grygorii Strashko
2016-09-14 20:43 ` Richard Cochran
2016-09-14 20:48 ` Grygorii Strashko
2016-09-14 13:02 ` [PATCH 9/9] net: ethernet: ti: cpts: switch to readl/writel_relaxed() Grygorii Strashko
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