On Thu, May 26, 2022 at 9:46 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Thu, May 26, 2022 at 11:54:22AM -0500, Bjorn Helgaas wrote: > > On Thu, May 05, 2022 at 08:10:43PM +0200, Rafael J. Wysocki wrote: > > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > > > > > Make pci_power_up() write 0 to the device's PCI_PM_CTRL register in > > > order to put it into D0 regardless of the power state returned by > > > the previous read from that register which should not matter. > > > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > > --- > > > drivers/pci/pci.c | 11 +++-------- > > > 1 file changed, 3 insertions(+), 8 deletions(-) > > > > > > Index: linux-pm/drivers/pci/pci.c > > > =================================================================== > > > --- linux-pm.orig/drivers/pci/pci.c > > > +++ linux-pm/drivers/pci/pci.c > > > @@ -1230,15 +1230,10 @@ int pci_power_up(struct pci_dev *dev) > > > } > > > > > > /* > > > - * If we're (effectively) in D3, force entire word to 0. This doesn't > > > - * affect PME_Status, disables PME_En, and sets PowerState to 0. > > > + * Force the entire word to 0. This doesn't affect PME_Status, disables > > > + * PME_En, and sets PowerState to 0. > > > */ > > > - if (state == PCI_D3hot) > > > - pmcsr = 0; > > > - else > > > - pmcsr &= ~PCI_PM_CTRL_STATE_MASK; > > > - > > > - pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, pmcsr); > > > + pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, 0); > > > > Can you reassure me why this is safe and useful? > > > > This is a 16-bit write that includes (PCIe r6.0, sec 7.5.2.2): > > > > 0x0003 PowerState RW > > 0x0004 RsvdP > > 0x0008 No_Soft_Reset RO > > 0x00f0 RsvdP > > 0x0100 PME_En RW/RWS > > 0x1e00 Data_Select RW, VF ROZ > > 0x6000 Data_Scale RO, VF ROZ > > 0x8000 PME_Status RW1CS > > > > We intend to set PowerState to 0 (D0), apparently intend to clear > > PME_En, and PME_Status is "write 1 to clear" to writing 0 does > > nothing, so those look OK. > > > > But the RsvdP fields are reserved for future RW bits and should be > > preserved, and it looks like clearing Data_Select could potentially > > break the Data Register power consumption reporting (which I don't > > think we support today). > > > > It seems like maybe we should do this instead: > > > > pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, > > pmcsr & ~PCI_PM_CTRL_STATE_MASK) > > > > to just unconditionally clear PowerState? > > Or I guess this, since we want to clear PME_En as well? > > pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, pmcsr & > ~(PCI_PM_CTRL_STATE_MASK | PCI_PM_CTRL_PME_ENABLE)); Yes. Also, this patch actually only makes a difference if the device is going into D0 from D1 or D2, because we have always written 0 to the PMCSR during transitions from D3hot. It is inconsistent and confusing to do different things depending on the initial power state here and the code is simpler when 0 is written regardless.
