Re: [PATCH] PCI/sysfs: Ensure devices are powered for config reads

[Ethan Zhao <etzhao1900@xxxxxxxxx>]

On 8/21/2025 1:26 AM, Brian Norris wrote:
> From: Brian Norris <briannorris@xxxxxxxxxx>
>
> max_link_speed, max_link_width, current_link_speed, current_link_width,
> secondary_bus_number, and subordinate_bus_number all access config
> registers, but they don't check the runtime PM state. If the device is
> in D3cold, we may see -EINVAL or even bogus values. 
My understanding, if your device is in D3cold, returning of -EINVAL is
the right behavior.  >
> Wrap these access in pci_config_pm_runtime_{get,put}() like most of the
> rest of the similar sysfs attributes.
>
> Fixes: 56c1af4606f0 ("PCI: Add sysfs max_link_speed/width, current_link_speed/width, etc")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Brian Norris <briannorris@xxxxxxxxxx>
> Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> ---
>
>   drivers/pci/pci-sysfs.c | 32 +++++++++++++++++++++++++++++---
>   1 file changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 5eea14c1f7f5..160df897dc5e 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -191,9 +191,16 @@ static ssize_t max_link_speed_show(struct device *dev,
>   				   struct device_attribute *attr, char *buf)
>   {
>   	struct pci_dev *pdev = to_pci_dev(dev);
> +	ssize_t ret;
> +
> +	pci_config_pm_runtime_get(pdev);
This function would potentially change the power state of device,
that would be a complex process, beyond the meaning of
max_link_speed_show(), given the semantics of these functions (
max_link_speed_show()/max_link_width_show()/current_link_speed_show()/
....),
this cannot be done !

Thanks,
Ethan>
> -	return sysfs_emit(buf, "%s\n",
> -			  pci_speed_string(pcie_get_speed_cap(pdev)));
> +	ret = sysfs_emit(buf, "%s\n",
> +			 pci_speed_string(pcie_get_speed_cap(pdev)));
> +
> +	pci_config_pm_runtime_put(pdev);
> +
> +	return ret;
>   }
>   static DEVICE_ATTR_RO(max_link_speed);
>   
> @@ -201,8 +208,15 @@ static ssize_t max_link_width_show(struct device *dev,
>   				   struct device_attribute *attr, char *buf)
>   {
>   	struct pci_dev *pdev = to_pci_dev(dev);
> +	ssize_t ret;
> +
> +	pci_config_pm_runtime_get(pdev);
> +
> +	ret = sysfs_emit(buf, "%u\n", pcie_get_width_cap(pdev));
>   
> -	return sysfs_emit(buf, "%u\n", pcie_get_width_cap(pdev));
> +	pci_config_pm_runtime_put(pdev);
> +
> +	return ret;
>   }
>   static DEVICE_ATTR_RO(max_link_width);
>   
> @@ -214,7 +228,10 @@ static ssize_t current_link_speed_show(struct device *dev,
>   	int err;
>   	enum pci_bus_speed speed;
>   
> +	pci_config_pm_runtime_get(pci_dev);
>   	err = pcie_capability_read_word(pci_dev, PCI_EXP_LNKSTA, &linkstat);
> +	pci_config_pm_runtime_put(pci_dev);
> +
>   	if (err)
>   		return -EINVAL;
>   
> @@ -231,7 +248,10 @@ static ssize_t current_link_width_show(struct device *dev,
>   	u16 linkstat;
>   	int err;
>   
> +	pci_config_pm_runtime_get(pci_dev);
>   	err = pcie_capability_read_word(pci_dev, PCI_EXP_LNKSTA, &linkstat);
> +	pci_config_pm_runtime_put(pci_dev);
> +
>   	if (err)
>   		return -EINVAL;
>   
> @@ -247,7 +267,10 @@ static ssize_t secondary_bus_number_show(struct device *dev,
>   	u8 sec_bus;
>   	int err;
>   
> +	pci_config_pm_runtime_get(pci_dev);
>   	err = pci_read_config_byte(pci_dev, PCI_SECONDARY_BUS, &sec_bus);
> +	pci_config_pm_runtime_put(pci_dev);
> +
>   	if (err)
>   		return -EINVAL;
>   
> @@ -263,7 +286,10 @@ static ssize_t subordinate_bus_number_show(struct device *dev,
>   	u8 sub_bus;
>   	int err;
>   
> +	pci_config_pm_runtime_get(pci_dev);
>   	err = pci_read_config_byte(pci_dev, PCI_SUBORDINATE_BUS, &sub_bus);
> +	pci_config_pm_runtime_put(pci_dev);
> +
>   	if (err)
>   		return -EINVAL;
>