From: Bjorn Helgaas <helgaas@kernel.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Linux PCI <linux-pci@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
Nathan Chancellor <nathan@kernel.org>,
Anders Roxell <anders.roxell@linaro.org>
Subject: Re: [PATCH v1 06/11] PCI/PM: Write 0 to PMCSR in pci_power_up() in all cases
Date: Fri, 27 May 2022 17:51:48 -0500 [thread overview]
Message-ID: <20220527225148.GA511276@bhelgaas> (raw)
In-Reply-To: <CAJZ5v0iteW2K0c7pS+ar1K_iL9L3ujQx=-ZRdrZFzxvkMVZorA@mail.gmail.com>
On Fri, May 27, 2022 at 08:52:17PM +0200, Rafael J. Wysocki wrote:
> On Thu, May 26, 2022 at 9:46 PM Bjorn Helgaas <helgaas@kernel.org> 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@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?
> >
> > 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.
I agree that depending on the initial power state is confusing (it
confused me :)).
What would you think of replacing this patch with the one below?
commit defde70748bc ("PCI/PM: Always put device in D0 and disable PME in pci_power_up()")
Author: Bjorn Helgaas <bhelgaas@google.com>
Date: Fri May 27 17:45:07 2022 -0500
PCI/PM: Always put device in D0 and disable PME in pci_power_up()
Unconditionally put the device in PCI_D0 and disable PME generation in
pci_power_up(), regardless of the power state returned by the previous read
from PCI_PM_CTRL, which should not matter.
Based-on-patch-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/5748066.MhkbZ0Pkbq@kreacher
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index a5b93f85377a..8e42a9dc1944 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1229,14 +1229,9 @@ int pci_power_up(struct pci_dev *dev)
goto end;
}
- /*
- * 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.
- */
- if (state == PCI_D3hot)
- pmcsr = 0;
- else
- pmcsr &= ~PCI_PM_CTRL_STATE_MASK;
+ /* Set PowerState to 0 (PCI_D0) and disable PME generation */
+ pmcsr &= ~PCI_PM_CTRL_STATE_MASK;
+ pmcsr &= ~PCI_PM_CTRL_PME_ENABLE;
pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, pmcsr);
next prev parent reply other threads:[~2022-05-27 22:51 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-05 17:57 [PATCH v1 00/11] PCI/PM: Rework powering up PCI devices Rafael J. Wysocki
2022-05-05 18:00 ` [PATCH v1 01/11] PCI/PM: Split pci_raw_set_power_state() Rafael J. Wysocki
2022-05-05 18:02 ` [PATCH v1 02/11] PCI/PM: Relocate pci_set_low_power_state() Rafael J. Wysocki
2022-05-05 18:04 ` [PATCH v1 03/11] PCI/PM: Set current_state to D3cold if the device is not accessible Rafael J. Wysocki
2022-05-05 18:05 ` [PATCH v1 04/11] PCI/PM: Unfold pci_platform_power_transition() in pci_power_up() Rafael J. Wysocki
2022-05-05 18:09 ` [PATCH v1 05/11] PCI/PM: Do not call pci_update_current_state() from pci_power_up() Rafael J. Wysocki
2022-05-05 18:10 ` [PATCH v1 06/11] PCI/PM: Write 0 to PMCSR in pci_power_up() in all cases Rafael J. Wysocki
2022-05-26 16:54 ` Bjorn Helgaas
2022-05-26 19:46 ` Bjorn Helgaas
2022-05-27 18:52 ` Rafael J. Wysocki
2022-05-27 22:51 ` Bjorn Helgaas [this message]
2022-05-27 23:09 ` Bjorn Helgaas
2022-05-28 13:59 ` Rafael J. Wysocki
2022-05-05 18:13 ` [PATCH v1 07/11] PCI/PM: Split pci_power_up() Rafael J. Wysocki
2022-05-05 18:14 ` [PATCH v1 08/11] PCI/PM: Do not restore BARs if device is not in D0 Rafael J. Wysocki
2022-05-05 18:15 ` [PATCH v1 09/11] PCI/PM: Clean up pci_set_low_power_state() Rafael J. Wysocki
2022-05-05 18:16 ` [PATCH v1 10/11] PCI/PM: Rearrange pci_set_power_state() Rafael J. Wysocki
2022-05-05 18:18 ` [PATCH v1 11/11] PCI/PM: Replace pci_set_power_state() in pci_pm_thaw_noirq() Rafael J. Wysocki
2022-05-05 19:22 ` [PATCH v1 00/11] PCI/PM: Rework powering up PCI devices Bjorn Helgaas
2022-05-05 19:44 ` Nathan Chancellor
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