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    SubjectRe: [linux-pm] Re: [RFC][PATCH 6/6] PCI PM: pci_save/restore_state improvements


    On Wed, 16 Nov 2005, Greg KH wrote:

    > On Wed, Nov 16, 2005 at 02:26:04AM -0500, Adam Belay wrote:
    > > On Tue, 2005-11-15 at 22:31 -0800, Greg KH wrote:
    > > > On Tue, Nov 15, 2005 at 10:31:42PM -0500, Adam Belay wrote:
    > > > > This patch makes some improvements to pci_save_state and
    > > > > pci_restore_state. Instead of saving and restoring all standard
    > > > > registers (even read-only ones), it only restores necessary registers.
    > > > > Also, the command register is handled more carefully. Let me know if
    > > > > I'm missing anything important.
    > > > >
    > > > >
    > > > > --- a/drivers/pci/pm.c 2005-11-13 20:32:24.000000000 -0500
    > > > > +++ b/drivers/pci/pm.c 2005-11-13 20:29:32.000000000 -0500
    > > > > @@ -53,10 +53,13 @@
    > > > > */
    > > > > int pci_save_state(struct pci_dev *dev)
    > > > > {
    > > > > - int i;
    > > > > - /* XXX: 100% dword access ok here? */
    > > > > - for (i = 0; i < 16; i++)
    > > > > - pci_read_config_dword(dev, i * 4,&dev->saved_config_space[i]);
    > > > > + struct pci_dev_config * conf = &dev->saved_config;
    > > > > +
    > > > > + pci_read_config_word(dev, PCI_COMMAND, &conf->command);
    > > > > + pci_read_config_byte(dev, PCI_CACHE_LINE_SIZE, &conf->cacheline_size);
    > > > > + pci_read_config_byte(dev, PCI_LATENCY_TIMER, &conf->latency_timer);
    > > > > + pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &conf->interrupt_line);
    > > >
    > > > Why are we saving and restoring smaller ammounts of config space now?
    > >
    > > After looking at the spec, it seems that most of the registers we were
    > > restoring were read-only and couldn't possibly need to be restored.
    > > Also, the PCI PM spec suggests that only a subset of the registers
    > > should be restored. Finally, things like BIST should probably never be
    > > touched.
    >
    > Ok, but be aware that this _might_ cause problems for some cards/drivers
    > that were relying on the old way... As long as you don't mind me
    > assigning those bugs to you, I don't have a problem with this :)

    If any drivers have bugs in that area, then they most likely only worked
    by accident in the first place. The confg space is mostly read-only
    anyway, and there could be things we don't want to blindly overwrite. If
    any drivers need more, they should save it themselves.



    Pat
    -
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