Re: [PATCH 1/4] PCI: qcom: Reshuffle reset logic in 2_7_0 .init

From: Konrad Dybcio <konrad.dybcio@linaro.org>
To: Johan Hovold <johan@kernel.org>
Cc: "Manivannan Sadhasivam" <mani@kernel.org>,
	"Bjorn Andersson" <andersson@kernel.org>,
	"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Rob Herring" <robh@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Philipp Zabel" <p.zabel@pengutronix.de>,
	"Stanimir Varbanov" <svarbanov@mm-sol.com>,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>,
	"Vinod Koul" <vkoul@kernel.org>,
	"Marijn Suijten" <marijn.suijten@somainline.org>,
	linux-arm-msm@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] PCI: qcom: Reshuffle reset logic in 2_7_0 .init
Date: Tue, 2 Jan 2024 18:03:36 +0100	[thread overview]
Message-ID: <07b20408-4b45-48c3-9356-730a7a827743@linaro.org> (raw)
In-Reply-To: <ZZPiwk1pbhLyfthB@hovoldconsulting.com>

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:
>>> [ Again, please remember to add a newline before you inline comments to
>>> make you replies readable. ]
>>>
>>> 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.
>>
>> diff --git a/drivers/clk/qcom/gcc-sc8280xp.c b/drivers/clk/qcom/gcc-sc8280xp.c
>> index 0b7801971dc1..6650bd6af5e3 100644
>> --- a/drivers/clk/qcom/gcc-sc8280xp.c
>> +++ b/drivers/clk/qcom/gcc-sc8280xp.c
>> @@ -7566,6 +7566,18 @@ static int gcc_sc8280xp_probe(struct platform_device *pdev)
>>         if (ret)
>>                 goto err_put_rpm;
>>  
>> +       int val;
>> +       regmap_read(regmap, 0xa0000, &val);
>> +       pr_err("GCC_PCIE_3A_BCR = 0x%x\n", val);
>> +       regmap_read(regmap, 0xa00f0, &val);
>> +       pr_err("GCC_PCIE_3A_LINK_DOWN_BCR = 0x%x\n", val);
>> +       regmap_read(regmap, 0xa00fc, &val);
>> +       pr_err("GCC_PCIE_3A_NOCSR_COM_PHY_BCR = 0x%x\n", val);
>> +       regmap_read(regmap, 0xa00e0, &val);
>> +       pr_err("GCC_PCIE_3A_PHY_BCR = 0x%x\n", val);
>> +       regmap_read(regmap, 0xa00e4, &val);
>> +       pr_err("GCC_PCIE_3A_PHY_NOCSR_COM_PHY_BCR = 0x%x\n", val);
>> +
>>         pm_runtime_put(&pdev->dev);
>>  
>>         return 0;
>>
>>
>> [root@sc8280xp-crd ~]# dmesg | grep BCR
>> [    2.500245] GCC_PCIE_3A_BCR = 0x0
>> [    2.500250] GCC_PCIE_3A_LINK_DOWN_BCR = 0x0
>> [    2.500253] GCC_PCIE_3A_NOCSR_COM_PHY_BCR = 0x0
>> [    2.500255] GCC_PCIE_3A_PHY_BCR = 0x0
>> [    2.500257] GCC_PCIE_3A_PHY_NOCSR_COM_PHY_BCR = 0x0
>>
>>
>> 0 meaning "not asserted".
> 
> 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.

> 
> 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."

> 
>> PCIE3A is used for WLAN on the CRD, btw.
> 
> You meant to say WWAN (modem).

Right :)

> 
>>>>>> Assert the reset (which may end up being a NOP if it was previously
>>>>>> asserted) and de-assert it back *before* turning on the clocks to avoid
>>>>>> such cases.
>>>>>>
>>>>>> In addition to that, in case the clock bulk enable fails, assert the
>>>>>> RC reset back, as the hardware is in an unknown state at best.
>>>>>
>>>>> This is arguably a separate change, and not necessarily one that is
>>>>> correct either
>>>
>>>> If the clock enable fails, the PCIe hw is not in reset state, ergo it
>>>> may be doing "something", and that "something" would eat non-zero power.
>>>> It's just cleaning up after yourself.
>>>
>>> How can it do something without power and clocks?
>>
>> Fair point.
>>
>> As far as power goes, the RC hangs off CX, which is on whenever the
>> system is not in power collapse. As for clocks, at least parts of it
>> use the crystal oscillator, not sure if directly.
>>
>>> And leaving reset
>>> asserted for non-powered devices is generally not a good idea.
>>
>> Depends on the hw.
> 
> That's why I said "generally".

I'll try to get a proper answer for this, or otherwise see if there's
any change in power draw / functionality.

Konrad