linux-kernel - Re: [tip: timers/core] clocksource/drivers/timer-probe: Avoid creating dead devices

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Date:   Thu, 26 Mar 2020 11:17:57 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Saravana Kannan <saravanak@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ionela Voinescu <ionela.voinescu@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-tip-commits@...r.kernel.org, x86 <x86@...nel.org>,
        liviu.dudau@....com, sudeep.holla@....com,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jon Hunter <jonathanh@...dia.com>
Subject: Re: [tip: timers/core] clocksource/drivers/timer-probe: Avoid
 creating dead devices


Hi Saravana,

On 25/03/2020 23:56, Saravana Kannan wrote:
> On Wed, Mar 25, 2020 at 2:47 PM Thomas Gleixner 
> <tglx@...utronix.de> wrote:
>> 
>> Saravana Kannan <saravanak@...gle.com> writes:
>>> On Tue, Mar 24, 2020 at 11:34 AM Saravana Kannan 
>>> <saravanak@...gle.com> wrote: I took a closer look. So two 
>>> different drivers [1] [2] are saying they know how to handle 
>>> "arm,vexpress-sysreg" and are expecting to run at the same 
>>> time. That seems a bit unusual to me. I wonder if this is a 
>>> violation of the device-driver model because this expectation 
>>> would never be allowed if these device drivers were actual 
>>> drivers registered with driver-core. But that's a discussion 
>>> for another time.
>>> 
>>> To fix this issue you are facing, this patch should work: 
>>> https://lore.kernel.org/lkml/20200324195302.203115-1-saravanak@google.com/T/#u
>>
>>
>>>
>>>
>>> 
> Sorry, that's not a fix. That's a crude hack.
> 
> If device nodes are being handled by drivers without binding a 
> driver to struct devices, then not setting OF_POPULATED is wrong. 
> So the original patch sets it. There are also very valid reasons 
> for allowing OF_POPULATED to be cleared by a driver as discussed 
> here [1].
> 
> The approach of the original patch (setting the flag and letting 
> the driver sometimes clear it) is also followed by many other 
> frameworks like irq, clk, i2c, etc. Even ingenic-timer.c already 
> does it for the exact same reason.
> 
> So, why is the vexpress fix a crude hack?
> 
>> As this is also causing trouble on tegra30-cardhu-a04 the only 
>> sane solution is to revert it and start over with a proper 
>> solution for the vexpress problem and a root cause analysis for 
>> the tegra.
> 
> If someone can tell me which of the timer drivers are relevant for 
> tegra30-cardhu-a04, I can help fix it. If you want to revert the 
> original patch first before waiting for a tegra fix, that's okay by
> me.


It seems the OF_POPULATED flag change spotted something wrong in
different drivers and that is a good thing. Thanks for your patch for
that.

Without putting in question your analysis, we need to stabilize the
release, can you send a revert of your patch?

Let's try to figure out what is happening and fix the issues in the
other drivers for the next cycle.

Thanks

  -- Daniel



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