linux-kernel - Re: [PATCH] clk-si544: Properly round requested frequency to nearest match

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Message-ID: <9eaa65c3-f8e0-1302-5f49-8691c244476d@topic.nl>
Date:   Fri, 1 Jun 2018 07:05:44 +0200
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     Stephen Boyd <sboyd@...nel.org>, <linux-clk@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <mturquette@...libre.com>
Subject: Re: [PATCH] clk-si544: Properly round requested frequency to nearest
 match

On 31-05-18 17:34, Stephen Boyd wrote:
> Quoting Mike Looijmans (2018-05-31 07:03:55)
>> The si544 driver had a rounding problem that using the result of clk_round_rate
>> may set the clock to yet another rate, for example:
>> clk_round_rate(195000000) = 194999999
>> clk_round_rate(194999999) = 194999998
>>
>> Clients would expect that after clk_set_rate(clk, freq2=clk_round_rate(clk, freq)) the
>> chip will be running at exactly freq2.
>>
>> The problem was in the calculation of the feedback divider, it was always rounded
>> down instead of to the nearest possible VCO value.
>>
>> After this change, the following holds true for any supported frequency:
>> actual_freq = clk_round_rate(clk, freq);
>> clk_set_rate(clk, actual_freq);
>> clk_round_rate(clk, actual_freq) == actual_freq && clk_get_rate(clk) == actual_freq
>>
>> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> 
> Any fixes tag? I can slap
> 
> Fixes: 953cc3e81170 ("clk: Add driver for the si544 clock generator chip")
> 
> on to the patch here.
> 

I think that would be good, yes. Slap it on.


Kind regards,

Mike Looijmans
System Expert

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