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

From: Richard Cochran
Date: Wed Sep 14 2016 - 17:03:43 EST

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

> if calculated results do not satisfy end user - the custom values can
> be passed in DT.

If we calculate automatically, then the result had better well be
optimal or nearly so. Otherwise, we should leave it as a manual input
via DTS, IMHO, so that someone is forced to check the values.