On Thu, Feb 13, 2025 at 03:52:05PM +0200, Ilpo Järvinen wrote:
> On Fri, 7 Feb 2025, Bjorn Helgaas wrote:
> > Many of the save/restore functions in the pci_save_state() and
> > pci_restore_state() paths depend on both a PCI capability of the device and
> > a pci_cap_saved_state structure to hold the configuration data, and they
> > skip the operation if either is missing.
> >
> > Look for the pci_cap_saved_state first so if we don't have one, we can skip
> > searching for the device capability, which requires several slow config
> > space accesses.
> > +++ b/drivers/pci/vc.c
> > @@ -355,20 +355,17 @@ int pci_save_vc_state(struct pci_dev *dev)
> > int i;
> >
> > for (i = 0; i < ARRAY_SIZE(vc_caps); i++) {
> > - int pos, ret;
> > struct pci_cap_saved_state *save_state;
> > + int pos, ret;
> > +
> > + save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> > + if (!save_state)
> > + return -ENOMEM;
> >
> > pos = pci_find_ext_capability(dev, vc_caps[i].id);
> > if (!pos)
> > continue;
> >
> > - save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> > - if (!save_state) {
> > - pci_err(dev, "%s buffer not found in %s\n",
> > - vc_caps[i].name, __func__);
> > - return -ENOMEM;
> > - }
>
> I think this order change will cause a functional change because
> pci_allocate_vc_save_buffers() only allocated for those capabilities that
> are exist for dev. Thus, the loop will prematurely exit.
Oof, thank you for catching this! I'll drop this for now.
It would be nice to make pci_save_vc_state() parallel with
pci_restore_vc_state() (and with most other pci_save_*_state()
functions) and have it return void. But pci_save_state() returns the
pci_save_vc_state() return value, and there are ~20 pci_save_state()
callers that pay attention to that return value.
I'm not convinced there's real value in pci_save_state() error
returns, given that so few callers check it, but it definitely
requires more analysis before removing it.
> > ret = pci_vc_do_save_buffer(dev, pos, save_state, true);
> > if (ret) {
> > pci_err(dev, "%s save unsuccessful %s\n",
> > @@ -392,12 +389,15 @@ void pci_restore_vc_state(struct pci_dev *dev)
> > int i;
> >
> > for (i = 0; i < ARRAY_SIZE(vc_caps); i++) {
> > - int pos;
> > struct pci_cap_saved_state *save_state;
> > + int pos;
> > +
> > + save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> > + if (!save_state)
> > + continue;
> >
> > pos = pci_find_ext_capability(dev, vc_caps[i].id);
> > - save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> > - if (!save_state || !pos)
> > + if (!pos)
> > continue;
> >
> > pci_vc_do_save_buffer(dev, pos, save_state, false);
> >
>
> --
> i.
>
