linux-kernel - Re: [PATCH 08/13] clk: qcom: hfpll: CLK_IGNORE

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:   Thu, 17 Jan 2019 11:46:21 +0100
From:   Jorge Ramirez <jorge.ramirez-ortiz@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>, robh+dt@...nel.org,
        mark.rutland@....com, andy.gross@...aro.org,
        david.brown@...aro.org, sboyd@...nel.org, will.deacon@....com,
        mturquette@...libre.com, jassisinghbrar@...il.com,
        vkoul@...nel.org, niklas.cassel@...aro.org, sibis@...eaurora.org,
        georgi.djakov@...aro.org, arnd@...db.de,
        horms+renesas@...ge.net.au, heiko@...ech.de,
        enric.balletbo@...labora.com, jagan@...rulasolutions.com,
        olof@...om.net, amit.kucheria@...aro.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH 08/13] clk: qcom: hfpll: CLK_IGNORE_UNUSED

On 1/17/19 11:08, Viresh Kumar wrote:
> On 17-01-19, 09:38, Jorge Ramirez wrote:
>> COMMON_CLK_DISABLED_UNUSED relies on the enable_count reference counter
>> to disable the clocks that were enabled by the firwmare and not by the
>> drivers.
>>
>> the cpufreq driver does not enable the cpu clock.
>>
>> so when clk_change_rate is called, the enable_count counter is not
>> incremented and therefore it just remains null since this was enabled by
>> the firmware.
>>
>> I tried doing:
>>
>> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
>> index e58bfcb..5a9f83e 100644
>> --- a/drivers/cpufreq/cpufreq-dt.c
>> +++ b/drivers/cpufreq/cpufreq-dt.c
>> @@ -124,6 +124,10 @@ static int resources_available(void)
>>                 return ret;
>>         }
>>
>> + ret = clk_prepare_enable(cpu_clk);
>> + if (ret)
>> +         return ret;
>> +
>>         clk_put(cpu_clk);
>>
>>         name = find_supply_name(cpu_dev);
>>
>>
>> and that removed the need for CLK_IGNORE_UNUSED. But I am not sure of
>> the system wide consequences of that change to cpufreq.
> 
> If the cpufreq driver enables it then it should disable it on exit as
> well, right ? And in that case if you unload your driver's module, you
> will hang the system as the clock will get disabled :)

ah, of course, sorry was over-thinking this thing :)

> 
> Every other platform must either be marking it with CLK_IGNORE_UNUSED
> or they must be doing clk_enable from somewhere, maybe the CPU online
> path, not sure though.
> 

since this clock is enabled by the firmware, it seems to me that using
CLK_IGNORE_UNUSED remains the best option.