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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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

TOPIC Products
Materiaalweg 4, NL-5681 RJ Best
Postbus 440, NL-5680 AK Best
Telefoon: +31 (0) 499 33 69 79
E-mail: mike.looijmans@...icproducts.com
Website: www.topicproducts.com

Please consider the environment before printing this e-mail