linux-kernel - Re: [PATCH 7/9] net: ethernet: ti: cpts: calc mult and shift from refclk freq

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Message-ID: <4d5308ae-02ea-e561-d190-350b994efef1@ti.com>
Date:   Thu, 15 Sep 2016 00:14:35 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Richard Cochran <richardcochran@...il.com>
CC:     "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        Mugunthan V N <mugunthanvnm@...com>,
        Sekhar Nori <nsekhar@...com>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>, WingMan Kwok <w-kwok2@...com>,
        John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 7/9] net: ethernet: ti: cpts: calc mult and shift from
 refclk freq

On 09/15/2016 12:03 AM, Richard Cochran wrote:
> On Wed, Sep 14, 2016 at 11:47:46PM +0300, Grygorii Strashko wrote:
>> As I understand (and tested), clocks_calc_mult_shift() will
>> return max possible mult which can be used without overflow.
>
> Yes, BUT the returned values depends on the @maxsec input.  As the
> kerneldec says,
>
>  * Larger ranges may reduce the conversion accuracy by chosing smaller
>  * mult and shift factors.
>
> In addition to that, frequency tuning by calculating a percentage of
> 'mult', and if 'mult' is small, then the tuning resolution is poor.
>
> So we don't want @maxsec as large as possible, but as small as
> possible.
>

Ok. So, will it work if maxsec will be ~= (maxsec / 2) + 1?
+ 1 to cover potential delays of overflow check work execution.

[...]


-- 
regards,
-grygorii