RE: [PATCH] PCI/ACPI: Disable AER when _OSC control bit is clear.

[Ghannam, Yazen]

> -----Original Message-----
> From: rjwysocki@xxxxxxxxx [mailto:rjwysocki@xxxxxxxxx] On Behalf Of
> Rafael J. Wysocki
> Sent: Thursday, January 11, 2018 12:39 PM
> To: Ghannam, Yazen <Yazen.Ghannam@xxxxxxx>
> Cc: ACPI Devel Maling List <linux-acpi@xxxxxxxxxxxxxxx>; Linux Kernel Mailing
> List <linux-kernel@xxxxxxxxxxxxxxx>; Linux PCI <linux-pci@xxxxxxxxxxxxxxx>;
> Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; Bjorn
> Helgaas <bhelgaas@xxxxxxxxxx>; Borislav Petkov <bp@xxxxxxx>
> Subject: Re: [PATCH] PCI/ACPI: Disable AER when _OSC control bit is clear.
> 
> On Thu, Jan 11, 2018 at 4:03 PM, Yazen Ghannam
> <Yazen.Ghannam@xxxxxxx> wrote:
> > From: Yazen Ghannam <yazen.ghannam@xxxxxxx>
> >
> > Currently, aer_service_init() checks if AER is available and that
> > Firmware First handling is not enabled. The _OSC request for AER is
> > not taken into account when deciding to enable AER in Linux.
> >
> > We should check that the _OSC control for AER is set. If it's not
> > then AER should be disabled.
> >
> > The _OSC control for AER is not requested when APEI Firmware First is
> > used, so the same condition applies.
> >
> > Mark AER as disabled if the _OSC request was not made or accepted.
> >
> > Remove redunant check for aer_acpi_firmware_first() when calling
> > aer_service_init(), since this is check is already included when
> > checking the _OSC control.
> >
> > Signed-off-by: Yazen Ghannam <yazen.ghannam@xxxxxxx>
> > ---
> >  drivers/acpi/pci_root.c       | 3 +++
> >  drivers/pci/pcie/aer/aerdrv.c | 2 +-
> >  2 files changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > index 6fc204a52493..19a625ed8de9 100644
> > --- a/drivers/acpi/pci_root.c
> > +++ b/drivers/acpi/pci_root.c
> > @@ -512,6 +512,9 @@ static void negotiate_os_control(struct
> acpi_pci_root *root, int *no_aspm)
> >                  */
> >                 *no_aspm = 1;
> >         }
> > +
> > +       if (!(requested & control & OSC_PCI_EXPRESS_AER_CONTROL))
> 
> One of the operators above needs to be a && I suppose?
> 

It's a 3-way bitwise AND to check that OSC_PCI_EXPRESS_AER_CONTROL is
set in both "requested" and "control".

IOW, we check if AER was requested by the OS and that the platform
granted the request.

Thanks,
Yazen