linux-kernel - Re: [PATCH] PCI: qcom: Prevent GDSC power down on suspend

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Message-ID: <zfs6krk2whthgdjl2s2w4o5pjwimzw37afoiyrqllykrk6jugt@4ijk5iqplohr>
Date: Wed, 28 Jan 2026 08:13:48 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Manivannan Sadhasivam <mani@...nel.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Stanimir Varbanov <svarbanov@...sol.com>, linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] PCI: qcom: Prevent GDSC power down on suspend

On Wed, Jan 28, 2026 at 05:52:42PM +0530, Krishna Chaitanya Chundru wrote:
> Currently, the driver expects the devices to remain in D0 across system
> suspend, but the genpd framework may still power down the associated
> GDSC during suspend. When that happens, the PCIe link goes down and
> cannot be recovered on resume.
> 

The GDSC is a child of CX, so by keeping it always-on, you effectively
put an always-on vote on CX, forever preventing CXPC.

In fact, this is one of the reasons why the PCIe GDSCs on most targets
is marked PWRSTS_RET_ON (in the clock driver) so that the "off state"
doesn't actually turn off the GDSC, but it relinquishes the inherited
vote on CX.

> Prevent genpd from turning off the PCIe GDSC by using
> dev_pm_genpd_rpm_always_on() so that the power domain stays on while
> the controller is suspended. This preserves the link state across
> suspend/resume and avoids unrecoverable link failures.
> 

We are able to suspend/resume a whole bunch of platforms today, which
one are you on?

That said, while we can suspend/resume, we're not allowing CXPC today.
On many systems the main culprit is the icc_set_bw() vote in
qcom_pcie_suspend_noirq().

Regards,
Bjorn

> Fixes: 82a823833f4e ("PCI: qcom: Add Qualcomm PCIe controller driver")
> Cc: stable@...r.kernel.org
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 5a318487b2b3f6c61d8f5b1fd5cdf2738a1f1dcd..314cf334a313dff35efaf0c023597e6eef483925 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -25,6 +25,7 @@
>  #include <linux/pci.h>
>  #include <linux/pci-ecam.h>
>  #include <linux/pm_opp.h>
> +#include <linux/pm_domain.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/platform_device.h>
>  #include <linux/phy/pcie.h>
> @@ -2052,6 +2053,11 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
>  		pcie->suspended = true;
>  	}
>  
> +	if (pcie->suspended)
> +		dev_pm_genpd_rpm_always_on(dev, false);
> +	else
> +		dev_pm_genpd_rpm_always_on(dev, true);
> +
>  	/*
>  	 * Only disable CPU-PCIe interconnect path if the suspend is non-S2RAM.
>  	 * Because on some platforms, DBI access can happen very late during the
> 
> ---
> base-commit: 1f97d9dcf53649c41c33227b345a36902cbb08ad
> change-id: 20260128-genpd_fix-3aa413d9a383
> 
> Best regards,
> -- 
> Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> 
>