linux-kernel - Re: [PATCH V2] cpufreq: tegra186: Fix initial frequency

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]

Message-ID: <382ba642-dbea-c36a-0c71-6e91ccb7b775@nvidia.com>
Date:   Wed, 28 Oct 2020 12:31:28 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Thierry Reding <thierry.reding@...il.com>,
        <linux-pm@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] cpufreq: tegra186: Fix initial frequency



On 28/10/2020 04:11, Viresh Kumar wrote:
> On 26-10-20, 12:57, Jon Hunter wrote:
>> Thinking about this some more, what are your thoughts on making the
>> following change? 
>>
>> Basically, if the driver sets the CPUFREQ_NEED_INITIAL_FREQ_CHECK,
> 
> This flag only means that the platform would like the core to check
> the currently programmed frequency and get it in sync with the table.

Yes exactly.

>> then I wonder if we should not fail if the frequency return by
>>> get() is not known.
> 
> When do we fail if the frequency isn't known ? That's the case where
> we try to set it to one from the table.

Currently, if the frequency is not known, we fail right before we do the
initial frequency check [0].

> But (looking at your change), ->get() can't really return 0. We depend
> on it to get us the exact frequency the hardware is programmed at
> instead of reading a cached value in the software.

Actually it can and it does currently. Note in tegra186_cpufreq_get()
the variable 'freq' is initialised to 0, and if no match is found, then
it returns 0. This is what happens currently on some Tegra186 boards.

>>> This would fix the problem I see on Tegra186
>> where the initial boot frequency may not be in the frequency table.
> 
> With current mainline, what's the problem you see now ? Sorry I missed
> track of it a bit :)

No problem, this has been an on-going saga now for sometime.

Cheers
Jon

[0]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/cpufreq/cpufreq.c#n1429
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/cpufreq/tegra186-cpufreq.c#n95

-- 
nvpublic