linux-kernel - Re: [PATCH v3 1/2] soc/tegra: pmc: Query PCLK clock rate at probe time

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 for Android: free password hash cracker in your pocket

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

Message-ID: <218c3d60-1a56-7ee8-840b-7d0559cd8c8e@gmail.com>
Date:   Fri, 2 Aug 2019 17:26:45 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter De Schrijver <pdeschrijver@...dia.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] soc/tegra: pmc: Query PCLK clock rate at probe
 time

02.08.2019 16:38, Peter De Schrijver пишет:
> On Tue, Jul 30, 2019 at 08:40:19PM +0300, Dmitry Osipenko wrote:
>> The PCLK clock is running off SCLK, which is a critical clock that is
>> very unlikely to randomly change its rate. It is possible to get a
>> lockup if kernel decides to enter LP2 cpuidle from a clk-notifier, which
>> happens occasionally in a case of Tegra30 EMC driver that waits for the
>> clk-change event in the clk-notify handler, because CCF's 'prepare' mutex
>> in kept locked and thus clk_get_rate() wants to sleep with interrupts
>> being disabled.
>>
> 
> I don't think this is the right solution. Eventually we will want to
> scale sclk and pclk because the clock tree power of those is not
> insignificant. Maybe register a notifier which updates the PMC timer
> values when pclk changes?

I also had a thought about the notifier for pclk, but wasn't sure if
it's really worthwhile right now since there is no real use-case and
it's not obvious when such case will materialize. So, I'd say that
solution is correct but incomplete.

I'll make a v4 with the notifier, since you're asking about it. Thanks
for the review!