| Message ID | 5748066.MhkbZ0Pkbq@kreacher |
|---|---|
| State | New |
| Headers | show |
| Series | PCI/PM: Rework powering up PCI devices | expand |
On Thu, May 05, 2022 at 08:10:43PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > 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@intel.com> > --- > 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?
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); /* Mandatory transition delays; see PCI PM 1.2. */ if (state == PCI_D3hot)