linux-kernel - Re: [PATCH] PCI, ACPI: Don't query OSC support with all possible controls

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Date:	Wed, 3 Apr 2013 17:00:59 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Len Brown <len.brown@...el.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bob Moore <robert.moore@...el.com>
Subject: Re: [PATCH] PCI, ACPI: Don't query OSC support with all possible controls

[+cc Bob for spec typo question]

On Wed, Mar 27, 2013 at 10:28 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> Found problem on system that firmware that could handle pci aer.
> Firmware get error reporting after pci injecting error, before os boots.
> But after os boots, firmware can not get report anymore, even pci=noaer
> is passed.
>
> Root cause: BIOS _OSC has problem with query bit checking.
> It turns out that BIOS vendor is copying example code from ACPI Spec.
> In ACPI Spec 5.0, page 290:
>
>         If (Not(And(CDW1,1))) // Query flag clear?
>         {       // Disable GPEs for features granted native control.
>                 If (And(CTRL,0x01)) // Hot plug control granted?
>                 {
>                         Store(0,HPCE) // clear the hot plug SCI enable bit
>                         Store(1,HPCS) // clear the hot plug SCI status bit
>                 }
>         ...
>         }
>
> When Query flag is set, And(CDW1,1) will be 1, Not(1) will return 0xfffffffe.
> So it will get into code path that should be for control set only.
> BIOS acpi code should be changed to "If (LEqual(And(CDW1,1), 0)))"

Isn't this just a typo in the spec?  Shouldn't it be using "LNot"
instead of "Not"?

         If (LNot(And(CDW1,1))) // Query flag clear?

Of course, that doesn't change the need for your Linux change, though
a comment about the hazard might be nice for future readers.

> Current kernel code is using _OSC query to notify firmware about support
> from OS and then use _OSC to set control bits.
> During query support, current code is using all possible controls.
> So will execute code that should be only for control set stage.
>
> That will have problem when pci=noaer or aer firmware_first is used.
> As firmware have that control set for os aer already in query support stage,
> but later will not os aer handling.
>
> We should avoid passing all possible controls, just use osc_control_set
> instead.
> That should workaround BIOS bugs with affected systems on the field
> as more bios vendors are copying sample code from ACPI spec.
>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> Cc: stable@...nel.org
>
> ---
>  drivers/acpi/pci_root.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/drivers/acpi/pci_root.c
> ===================================================================
> --- linux-2.6.orig/drivers/acpi/pci_root.c
> +++ linux-2.6/drivers/acpi/pci_root.c
> @@ -201,8 +201,8 @@ static acpi_status acpi_pci_query_osc(st
>                 *control &= OSC_PCI_CONTROL_MASKS;
>                 capbuf[OSC_CONTROL_TYPE] = *control | root->osc_control_set;
>         } else {
> -               /* Run _OSC query for all possible controls. */
> -               capbuf[OSC_CONTROL_TYPE] = OSC_PCI_CONTROL_MASKS;
> +               /* Run _OSC query only with existing controls. */
> +               capbuf[OSC_CONTROL_TYPE] = root->osc_control_set;
>         }
>
>         status = acpi_pci_run_osc(root->device->handle, capbuf, &result);
--
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