linux-kernel - Re: [PATCH 1/4] PCI: qcom: Reshuffle reset logic in 2_7

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Message-ID: <bd75f372-8ffe-415f-9464-3b78fd92e3f9@linaro.org>
Date: Wed, 3 Jan 2024 13:11:12 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Manivannan Sadhasivam <mani@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Philipp Zabel <p.zabel@...gutronix.de>,
 Stanimir Varbanov <svarbanov@...sol.com>,
 Andrew Murray <amurray@...goodpenguin.co.uk>, Vinod Koul <vkoul@...nel.org>,
 Marijn Suijten <marijn.suijten@...ainline.org>,
 linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] PCI: qcom: Reshuffle reset logic in 2_7_0 .init

On 3.01.2024 11:40, Johan Hovold wrote:
> On Tue, Jan 02, 2024 at 06:03:36PM +0100, Konrad Dybcio wrote:
>> On 2.01.2024 11:17, Johan Hovold wrote:
>>> On Sat, Dec 30, 2023 at 02:16:18AM +0100, Konrad Dybcio wrote:
>>>> On 29.12.2023 16:29, Johan Hovold wrote:
>>>>> On Fri, Dec 29, 2023 at 04:01:27PM +0100, Konrad Dybcio wrote:
>>>>>> On 29.12.2023 15:04, Johan Hovold wrote:
>>>>>>> On Wed, Dec 27, 2023 at 11:17:19PM +0100, Konrad Dybcio wrote:
>>>>>>>> At least on SC8280XP, if the PCIe reset is asserted, the corresponding
>>>>>>>> AUX_CLK will be stuck at 'off'.
>>>>>>>
>>>>>>> No, this path is exercised on every boot without the aux clock ever
>>>>>>> being stuck at off. So something is clearly missing in this description.
>>>>>
>>>>>> That's likely because the hardware has been initialized and not cleanly
>>>>>> shut down by your bootloader. When you reset it, or your bootloader
>>>>>> wasn't so kind, you need to start initialization from scratch.
>>>>>
>>>>> What does that even mean? I'm telling you that this reset is asserted on
>>>>> each boot, on all sc8280xp platforms I have access to, and never have I
>>>>> seen the aux clk stuck at off.
>>>>>
>>>>> So clearly your claim above is too broad and the commit message is
>>>>> incorrect or incomplete.
> 
>>> We're clearly talking past each other. When I'm saying reset is asserted
>>> on each boot, I'm referring to reset being asserted in
>>> qcom_pcie_init_2_7_0(), whereas you appear to be referring to whether
>>> the reset has been left asserted by the bootloader when the driver
>>> probes.
>>
>> OK, "boot" meant "booting the device" to me, not the PCIe controller.
> 
> Still not getting across to you apparently.
> 
> Again, the code in question is exercised on every boot and not once have
> I seen a stuck clock due to reset being asserted *in*
> qcom_pcie_init_2_7_0().
> 
> Now that's not what you were trying to describe as you were thinking of
> reset having been left asserted *before* the driver probes (or before
> qcom_pcie_init_2_7_0() is called).
> 
> See? Do you understand now what I was trying to say and why my
> misinterpretation of your terse commit message lead me to claim that it
> was clearly false?

No, my response was an acknowledgement of having understood you. Maybe
it's a direct translation of some Polish idiom that's not obvious to
others, but I definitely tried to say that "we were talking about
different things, I had been previously thinking of something else,
but now we're on the same page".


> 
>>> I understand what you meant to say now, but I think you should rephrase:
>>>
>>> 	At least on SC8280XP, if the PCIe reset is asserted, the
>>> 	corresponding AUX_CLK will be stuck at 'off'.
>>>
>>> because as it stands, it sounds like the problem happens when the driver
>>> asserts reset.
>>
>> Does this sound good?
>>
>> "At least on SC8280XP, trying to enable the AUX_CLK associated with
>> a PCIe host fails if the corresponding PCIe reset is asserted."
> 
> Yes, but you need to also say something about how this would happen, for
> example, your hypothetical bootloader leaving it asserted and your actual
> motivation for this change which is that it appears to be needed after
> suspend. 
> 
> A commit message should be clear and self-contained and not force
> reviewers to have to try to interpret what it means and guess what the
> motivation for the change really is.

Got it

Konrad