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From: Bjorn Helgaas <helgaas@kernel.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: 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: Thu, 26 May 2022 14:46:01 -0500	[thread overview]
Message-ID: <20220526194601.GA344086@bhelgaas> (raw)
In-Reply-To: <20220526165422.GA338382@bhelgaas>

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));

  reply	other threads:[~2022-05-26 19:46 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 [this message]
2022-05-27 18:52       ` Rafael J. Wysocki
2022-05-27 22:51         ` Bjorn Helgaas
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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