linux-kernel - Re: [PATCH 0/4] PCI/pwrctrl: Rework pwrctrl driver integration and add driver for PCI slot

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Message-ID: <20241216052107.tyhwzh4g3tmnp5ll@thinkpad>
Date: Mon, 16 Dec 2024 10:51:07 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Lukas Wunner <lukas@...ner.de>
Cc: Qiang Yu <quic_qianyu@...cinc.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Bartosz Golaszewski <brgl@...ev.pl>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>
Subject: Re: [PATCH 0/4] PCI/pwrctrl: Rework pwrctrl driver integration and
 add driver for PCI slot

On Sun, Dec 15, 2024 at 06:32:02PM +0100, Lukas Wunner wrote:
> On Wed, Dec 11, 2024 at 05:55:48PM +0800, Qiang Yu wrote:
> > PCIe3 is able to link up after applying your patch. Slot power is turned on
> > correctly.
> > But see "NULL pointer dereference" when I try to remove device.
> 
> There's a WARN splat occurring before the NULL pointer deref.
> Was this happening before or is it new?  Probably makes sense
> to debug that first before looking into the NULL pointer deref,
> which could be a result of it.
> 

Precisely.

> 
> > [   38.757726] WARNING: CPU: 1 PID: 816 at drivers/regulator/core.c:5857
> > regulator_unregister+0x13c/0x160
> > [   38.767288] Modules linked in: phy_qcom_qmp_combo aux_bridge
> > drm_kms_helper drm nvme backlight pinctrl_sm8550_lpass_lpi pci_pwrctl_slot
> > pci_pwrctrl_core nvme_core phy_qcom_edp phy_qcom_eusb2_repeater
> > dispcc_x1e80100 pinctrl_lpass_lpi phy_qcom_snps_eusb2 lpasscc_sc8280xp typec
> > gpucc_x1e80100 phy_qcom_qmp_pcie
> > [   38.795279] CPU: 1 UID: 0 PID: 816 Comm: bash Not tainted
> > 6.12.0-next-20241128-00005-g6178bf6ce3c2-dirty #50
> > [   38.805359] Hardware name: Qualcomm IDP, BIOS
> > 6.0.240607.BOOT.MXF.2.4-00348.1-HAMOA-1.67705.7 06/ 7/2024
> > [   38.815088] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS
> > BTYPE=--)
> > [   38.822239] pc : regulator_unregister+0x13c/0x160
> > [   38.827081] lr : regulator_unregister+0xc0/0x160
> 
> The WARN splat seems to be caused by:
> 
> 	WARN_ON(rdev->open_count);
> 
> So the regulator is unregistered although it's still in use.
> Is there maybe a multifunction PCIe device in your system
> so that multiple devices are using the same regulator?
> 

Maybe the regulator is shared with other peripherals (not just PCIe) in the
system.

@Qiang: I referred your patch [1] that added the slot regulators, but they were
not used by any peripherals other than PCIe. Could you please post the list of
consumers of the 3 slot regulators?

FYI, I did test root port remove on RB5 board (with dummy fixed regulators) and
it worked fine.

- Mani

[1] https://lore.kernel.org/linux-pci/20240827063631.3932971-8-quic_qianyu@quicinc.com/

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