Re: [PATCH v2] PCI/PTM: Do not enable PTM solely based on the capability existense

[Lukas Wunner <lukas@wunner.de>]

On Wed, Oct 29, 2025 at 06:33:54AM +0100, Mika Westerberg wrote:
> On Tue, Oct 28, 2025 at 12:06:39PM -0500, Bjorn Helgaas wrote:
> > On Tue, Oct 28, 2025 at 07:04:27AM +0100, Mika Westerberg wrote:
> > > @@ -125,7 +140,7 @@ static int __pci_enable_ptm(struct pci_dev *dev)
> > >  {
> > >  	u16 ptm = dev->ptm_cap;
> > >  	struct pci_dev *ups;
> > > -	u32 ctrl;
> > > +	u32 cap, ctrl;
> > >  
> > >  	if (!ptm)
> > >  		return -EINVAL;
> > > @@ -144,6 +159,14 @@ static int __pci_enable_ptm(struct pci_dev *dev)
> > >  			return -EINVAL;
> > >  	}
> > >  
> > > +	/*
> > > +	 * PCIe Endpoint must declare Requester Capable before we can
> > > +	 * enable PTM for it.
> > > +	 */
> > > +	pci_read_config_dword(dev, ptm + PCI_PTM_CAP, &cap);
> > > +	if (!(cap & PCI_PTM_CAP_REQ))
> > > +		return -EINVAL;
> > 
> > Isn't this going to prevent enabling PTM on Root Ports?
> 
> Isn't this function called only for Endpoints? Root Ports and Switch Ports
> are enabled in pci_ptm_init() instead.

The function is also called for Root Ports:

  pci_ptm_init()
    pci_enable_ptm()
      __pci_enable_ptm()

So I guess you need to constrain this to:

  PCI_EXP_TYPE_ENDPOINT
  PCI_EXP_TYPE_LEG_END

Sorry for missing that during review!

Lukas