linux-kernel - Re: [PATCH V7 0/2] qcom: x1e80100: Enable CPUFreq

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Message-ID: <48cfd337-e691-7f10-71df-f6389e098e67@quicinc.com>
Date: Fri, 17 Jan 2025 12:06:29 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Johan Hovold <johan@...nel.org>
CC: Marc Zyngier <maz@...nel.org>, <sudeep.holla@....com>,
        <cristian.marussi@....com>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <dmitry.baryshkov@...aro.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <quic_rgottimu@...cinc.com>,
        <quic_kshivnan@...cinc.com>, <conor+dt@...nel.org>,
        <quic_nkela@...cinc.com>, <quic_psodagud@...cinc.com>,
        <abel.vesa@...aro.org>
Subject: Re: [PATCH V7 0/2] qcom: x1e80100: Enable CPUFreq



On 1/10/25 15:22, Johan Hovold wrote:
> On Mon, Jan 06, 2025 at 05:52:48PM +0530, Sibi Sankar wrote:
>> On 12/5/24 21:16, Johan Hovold wrote:
> 
>>> As Marc said, it seems you need to come up with a way to detect and work
>>> around the broken firmware.
>>
>> The perf protocol version won't have any changes so detecting
>> it isn't possible :(
> 
> But there could be other ways, see below.
> 
>>> We want to get the fast channel issue fixed, but when we merge that fix
>>> it will trigger these crashes if we also merge cpufreq support for x1e.
>>>
>>> Can you expand the on the PERF_LEVEL_GET issue? Is it possible to
>>> implement some workaround for the buggy firmware? Like returning a dummy
>>> value? How exactly are things working today? Can't that be used a basis
>>> for a quirk?
>>
>> The main problem is the X1E firmware supports fast channel level get
>> but when queried it says it doesn't support it :|. The PERF_LEVEL_GET
>> regular messaging which gets used as a fallback has a bug which causes
>> the device to crash. So we either enable cpufreq only on platforms
>> that has the fix in place or live with the warning that certain messages
>> don't support fast channel which I don't think will fly. I've also been
>> told the crash wouldn't show up if we have all sleep states disabled.
> 
> We certainly want cpufreq enabled also on the current/older firmware
> which have these bugs.
> 
> Based on the above, it sounds like your fix:
> 
> 	https://lore.kernel.org/lkml/20241030125512.2884761-2-quic_sibis@quicinc.com/
> 
> is correct even if it triggers the crash on machines with buggy firmware.
> 
> Why can't you add a quirk for x1e platforms that makes sure that the
> driver always uses fastchannel level get?

Makes sense but introducing anything like ^^ needs consensus from
the scmi maintainers but for obvious they won't comment on this
thread :| . I'll repeat the same question on another thread.

-Sibi

> 
> You know it is supported (and as has to be used) even if the buggy
> firmware says it's not. Just set the corresponding attribute bit
> unconditionally based on the DT machine compatible (or fall back to the
> current implementation which theoretically other broken fw
> implementations may also be relying on), or similar.
> 
> Johan