linux-kernel - Re: [PATCH] PCI: dwc: Enable runtime pm of the host bridge

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Message-ID: <20240226155305.GJ8422@thinkpad>
Date: Mon, 26 Feb 2024 21:23:05 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc: Jingoo Han <jingoohan1@...il.com>,
	Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	quic_vbadigan@...cinc.com, quic_ramkri@...cinc.com,
	quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
	quic_parass@...cinc.com
Subject: Re: [PATCH] PCI: dwc: Enable runtime pm of the host bridge

On Mon, Feb 19, 2024 at 06:51:10PM +0530, Krishna chaitanya chundru wrote:
> Currently controller driver goes to runtime suspend irrespective
> of the child(pci-pci bridge & endpoint driver) runtime state.
> This is because the runtime pm is not being enabled for the host
> bridge dev which maintains parent child relationship.
> 

You should describe the parent-child topology first. Maybe a simple flow like
below will help:

	PCIe Controller
	      |
	PCIe Host bridge
	      |
	PCI-PCI bridge
	      |
	PCIe endpoint

Also explain the fact that since runtime PM is disabled for host bridge, the
state of the child devices under the host bridge is not taken into account by
PM framework for the top level parent, PCIe controller. So PM framework, allows
the controller driver to enter runtime PM irrespective of the state of the
devices under the host bridge. And this causes the topology breakage and also
possible PM issues.

- Mani

> So enable pm runtime for the host bridge, so that controller driver
> goes to suspend only when all child devices goes to runtime suspend.
> 
> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index d5fc31f8345f..57756a73df30 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -16,6 +16,7 @@
>  #include <linux/of_pci.h>
>  #include <linux/pci_regs.h>
>  #include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
>  
>  #include "../../pci.h"
>  #include "pcie-designware.h"
> @@ -505,6 +506,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  	if (pp->ops->post_init)
>  		pp->ops->post_init(pp);
>  
> +	pm_runtime_set_active(&bridge->dev);
> +	pm_runtime_enable(&bridge->dev);
> +
>  	return 0;
>  
>  err_stop_link:
> 
> ---
> base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
> change-id: 20240219-runtime_pm_enable-bdc17914bd50
> 
> Best regards,
> -- 
> Krishna chaitanya chundru <quic_krichai@...cinc.com>
> 

-- 
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