Re: [PATCH v2] PCI: Make d3cold_allowed sysfs attribute read only

[Mario Limonciello <mario.limonciello@xxxxxxx>]

On 10/5/2023 13:53, Bjorn Helgaas wrote:
> On Wed, Oct 04, 2023 at 09:47:31AM -0500, Mario Limonciello wrote:
> > Before d3cold was stable userspace was allowed to influence the kernel's
> > decision of whether to enable d3cold for a device by a sysfs file
> > `d3cold_allowed`.  This potentially allows userspace to break the suspend
> > for the system.
>
> Is "Before d3cold was stable" referring to a "d3cold" read-only
> variable, or to Linux functionality of using D3cold, or ...?

I was referring to the previous thread's comments when I asked about the 
history on it.

> In what sense does the `d3cold_allowed` sysfs file break suspend?

SoCs might not be able to get into their deepest sleep state if 
userspace messes with it.

> > For debugging purposes `pci_port_pm=` can be used to control whether
> > a PCI port will go into D3cold and runtime PM can be turned off by
> > sysfs on PCI end points.
>
> I guess this should be "pcie_port_pm=", which affects *all* PCIe
> ports?

Yes.

> Which sysfs file turns off runtime PM for endpoints?

/sys/bus/pci/devices/*/power/control

> > Change the sysfs attribute to a noop that ignores the input when written
> > and shows a warning. Simplify the internal kernel logic to drop
> > `d3cold_allowed`.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> > v1->v2:
> >   * Leave R/W and show a warning instead
> >   * Mark deprecated in sysfs file
> > ---
> >   Documentation/ABI/testing/sysfs-bus-pci |  4 ++--
> >   drivers/pci/pci-acpi.c                  |  2 +-
> >   drivers/pci/pci-sysfs.c                 | 14 ++------------
> >   drivers/pci/pci.c                       |  3 +--
> >   include/linux/pci.h                     |  1 -
> >   5 files changed, 6 insertions(+), 18 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> > index ecf47559f495..b5db141dfee6 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-pci
> > +++ b/Documentation/ABI/testing/sysfs-bus-pci
> > @@ -283,8 +283,8 @@ Description:
> >   		device will never be put into D3Cold state.  If it is set, the
> >   		device may be put into D3Cold state if other requirements are
> >   		satisfied too.  Reading this attribute will show the current
> > -		value of d3cold_allowed bit.  Writing this attribute will set
> > -		the value of d3cold_allowed bit.
> > +		value of no_d3cold bit.
> > +		Writing to this attribute is deprecated and will do nothing.
> >   
> >   What:		/sys/bus/pci/devices/.../sriov_totalvfs
> >   Date:		November 2012
> > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> > index 05b7357bd258..a05350a4e49c 100644
> > --- a/drivers/pci/pci-acpi.c
> > +++ b/drivers/pci/pci-acpi.c
> > @@ -911,7 +911,7 @@ pci_power_t acpi_pci_choose_state(struct pci_dev *pdev)
> >   {
> >   	int acpi_state, d_max;
> >   
> > -	if (pdev->no_d3cold || !pdev->d3cold_allowed)
> > +	if (pdev->no_d3cold)
> >   		d_max = ACPI_STATE_D3_HOT;
> >   	else
> >   		d_max = ACPI_STATE_D3_COLD;
> > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > index 5e741a05cf2c..52ed5a55a371 100644
> > --- a/drivers/pci/pci-sysfs.c
> > +++ b/drivers/pci/pci-sysfs.c
> > @@ -523,17 +523,7 @@ static ssize_t d3cold_allowed_store(struct device *dev,
> >   				    struct device_attribute *attr,
> >   				    const char *buf, size_t count)
> >   {
> > -	struct pci_dev *pdev = to_pci_dev(dev);
> > -	unsigned long val;
> > -
> > -	if (kstrtoul(buf, 0, &val) < 0)
> > -		return -EINVAL;
> > -
> > -	pdev->d3cold_allowed = !!val;
> > -	pci_bridge_d3_update(pdev);
> > -
> > -	pm_runtime_resume(dev);
> > -
> > +	dev_warn_once(dev, "pci: writing to d3cold_allowed is deprecated\n");
> >   	return count;
> >   }
> >   
> > @@ -541,7 +531,7 @@ static ssize_t d3cold_allowed_show(struct device *dev,
> >   				   struct device_attribute *attr, char *buf)
> >   {
> >   	struct pci_dev *pdev = to_pci_dev(dev);
> > -	return sysfs_emit(buf, "%u\n", pdev->d3cold_allowed);
> > +	return sysfs_emit(buf, "%u\n", !pdev->no_d3cold);
> >   }
> >   static DEVICE_ATTR_RW(d3cold_allowed);
> >   #endif
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 59c01d68c6d5..8c5a6f68f63d 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -3067,7 +3067,7 @@ static int pci_dev_check_d3cold(struct pci_dev *dev, void *data)
> >   	bool *d3cold_ok = data;
> >   
> >   	if (/* The device needs to be allowed to go D3cold ... */
> > -	    dev->no_d3cold || !dev->d3cold_allowed ||
> > +	    dev->no_d3cold ||
> >   
> >   	    /* ... and if it is wakeup capable to do so from D3cold. */
> >   	    (device_may_wakeup(&dev->dev) &&
> > @@ -3204,7 +3204,6 @@ void pci_pm_init(struct pci_dev *dev)
> >   	dev->d3hot_delay = PCI_PM_D3HOT_WAIT;
> >   	dev->d3cold_delay = PCI_PM_D3COLD_WAIT;
> >   	dev->bridge_d3 = pci_bridge_d3_possible(dev);
> > -	dev->d3cold_allowed = true;
> >   
> >   	dev->d1_support = false;
> >   	dev->d2_support = false;
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 8c7c2c3c6c65..5f4ed71d31f5 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -376,7 +376,6 @@ struct pci_dev {
> >   	unsigned int	no_d1d2:1;	/* D1 and D2 are forbidden */
> >   	unsigned int	no_d3cold:1;	/* D3cold is forbidden */
> >   	unsigned int	bridge_d3:1;	/* Allow D3 for bridge */
> > -	unsigned int	d3cold_allowed:1;	/* D3cold is allowed by user */
> >   	unsigned int	mmio_always_on:1;	/* Disallow turning off io/mem
> >   						   decoding during BAR sizing */
> >   	unsigned int	wakeup_prepared:1;
> > --
> > 2.34.1