linux-kernel - Re: [PATCH] PCI: Call _REG when saving/restoring PCI state

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Message-ID: <ZHpPOzT0nm+vddPq@bhelgaas>
Date:   Fri, 2 Jun 2023 15:21:15 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH] PCI: Call _REG when saving/restoring PCI state

[+cc Rafael, Len, linux-acpi]

Hi Mario,

On Thu, Jun 01, 2023 at 10:11:22PM -0500, Mario Limonciello wrote:
> ASMedia PCIe GPIO controllers connected to AMD SOC fail functional tests
> after returning from s2idle. This is because the BIOS checks whether the
> OSPM has called the _REG method to determine whether it can interact with
> the OperationRegion assigned to the device.

"s2idle" is a Linux term; I'd prefer something that we can relate to
the ACPI spec.

Maybe a pointer to the specific function in the driver that has a
problem?  Based on the patch, I assume the driver uses some control
method that looks at PCI config space?

> To fix this issue, call acpi_evaluate_reg() when saving and restoring the
> state of PCI devices.

Please include the spec citation: ACPI r6.5, sec 6.5.4.  The URL has
changed in the past and may change in the future, but the name/section
number will not.

> Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/06_Device_Configuration/Device_Configuration.html#reg-region
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  drivers/pci/pci.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e38c2f6eebd4..071ecba548b0 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1068,6 +1068,12 @@ static inline bool platform_pci_bridge_d3(struct pci_dev *dev)
>  	return acpi_pci_bridge_d3(dev);
>  }
>  
> +static inline int platform_toggle_reg(struct pci_dev *dev, int c)
> +{
> +	return acpi_evaluate_reg(ACPI_HANDLE(&dev->dev),
> +				 ACPI_ADR_SPACE_PCI_CONFIG, c);
> +}

You never check the return value, so why return it?

The function actually doesn't *toggle*; it connects or disconnects
based on "c".

This looks like it only builds when CONFIG_ACPI=y?

>  /**
>   * pci_update_current_state - Read power state of given device and cache it
>   * @dev: PCI device to handle.
> @@ -1645,6 +1651,9 @@ static void pci_restore_ltr_state(struct pci_dev *dev)
>  int pci_save_state(struct pci_dev *dev)
>  {
>  	int i;
> +
> +	platform_toggle_reg(dev, ACPI_REG_DISCONNECT);

I would expect these to be in the PM code near the power state
transitions, not in the state save/restore code.  These functions
*are* used during suspend/resume, but are used in other places as
well, where we probably don't want _REG executed.

Cc'd Rafael and PM folks, who can give much better feedback.

>  	/* XXX: 100% dword access ok here? */
>  	for (i = 0; i < 16; i++) {
>  		pci_read_config_dword(dev, i * 4, &dev->saved_config_space[i]);
> @@ -1790,6 +1799,8 @@ void pci_restore_state(struct pci_dev *dev)
>  	pci_enable_acs(dev);
>  	pci_restore_iov_state(dev);
>  
> +	platform_toggle_reg(dev, ACPI_REG_CONNECT);
> +
>  	dev->state_saved = false;
>  }
>  EXPORT_SYMBOL(pci_restore_state);
> @@ -3203,6 +3214,7 @@ void pci_pm_init(struct pci_dev *dev)
>  	pci_read_config_word(dev, PCI_STATUS, &status);
>  	if (status & PCI_STATUS_IMM_READY)
>  		dev->imm_ready = 1;
> +	platform_toggle_reg(dev, ACPI_REG_CONNECT);
>  }
>  
>  static unsigned long pci_ea_flags(struct pci_dev *dev, u8 prop)
> -- 
> 2.34.1
>