linux-kernel - Re: [PATCH v9 2/7] PCI: Add assert_perst() operation to control PCIe PERST#

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Message-ID: <prngl7yl7rveyp76ksmskzgv2oigayrhz4s5fnlz7iycae3kkp@v6fn54ybwrec>
Date: Sat, 1 Nov 2025 10:34:58 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Jingoo Han <jingoohan1@...il.com>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konradybcio@...nel.org>, cros-qcom-dts-watchers@...omium.org, linux-pci@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v9 2/7] PCI: Add assert_perst() operation to control PCIe
 PERST#

On Sat, Nov 01, 2025 at 09:29:33AM +0530, Krishna Chaitanya Chundru wrote:
> Controller driver probes firsts, enables link training and scans the
> bus. When the PCI bridge is found, its child DT nodes will be scanned
> and pwrctrl devices will be created if needed. By the time pwrctrl
> driver probe gets called link training is already enabled by controller
> driver.
> 
> Certain devices like TC9563 which uses PCI pwrctl framework needs to
> configure the device before PCI link is up.
> 
> As the controller driver already enables link training as part of
> its probe, the moment device is powered on, controller and device
> participates in the link training and link can come up immediately
> and may not have time to configure the device.
> 
> So we need to stop the link training by using assert_perst() by asserting
> the PERST# and de-assert the PERST# after device is configured.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>

Acked-by: Manivannan Sadhasivam <mani@...nel.org>

- Mani

> ---
>  include/linux/pci.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index d1fdf81fbe1e427aecbc951fa3fdf65c20450b05..ed5dac663e96e3a6ad2edffffc9fa8b348d0a677 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -829,6 +829,7 @@ struct pci_ops {
>  	void __iomem *(*map_bus)(struct pci_bus *bus, unsigned int devfn, int where);
>  	int (*read)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 *val);
>  	int (*write)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 val);
> +	int (*assert_perst)(struct pci_bus *bus, bool assert);
>  };
>  
>  /*
> 
> -- 
> 2.34.1
> 

-- 
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