Re: [PATCH 1/3] PCI/AER: Option to leave System Error Interrupts as-is

Borislav Petkov
2018-11-02T09:53:08Z

On Mon, Oct 29, 2018 at 04:06:51PM -0500, Bjorn Helgaas wrote:
> [+cc Rafael, Len, Tony, Borislav, Tyler, Christoph, linux-acpi, LKML]
>
> On Fri, Oct 26, 2018 at 02:19:04PM -0600, Jon Derrick wrote:
> > Add a bit in pci_host_bridge to indicate to leave the System Error
> > Interrupts as configured by the pre-boot environment. Propagate this to
> > the AER driver which disables System Error Interrupts.

This commit message should not explain what the patch does - that's
obvious - but why it is doing it.

> > Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
> > ---
> > drivers/pci/pcie/aer.c | 7 +++++--
> > include/linux/pci.h | 3 +++
> > 2 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> > index 83180ed..6a4af63 100644
> > --- a/drivers/pci/pcie/aer.c
> > +++ b/drivers/pci/pcie/aer.c
> > @@ -1360,6 +1360,7 @@ static void set_downstream_devices_error_reporting(struct pci_dev *dev,
> > static void aer_enable_rootport(struct aer_rpc *rpc)
> > {
> > struct pci_dev *pdev = rpc->rpd;
> > + struct pci_host_bridge *host;
> > int aer_pos;
> > u16 reg16;
> > u32 reg32;
> > @@ -1369,8 +1370,10 @@ static void aer_enable_rootport(struct aer_rpc *rpc)
> > pcie_capability_write_word(pdev, PCI_EXP_DEVSTA, reg16);
> >
> > /* Disable system error generation in response to error messages */
> > - pcie_capability_clear_word(pdev, PCI_EXP_RTCTL,
> > - SYSTEM_ERROR_INTR_ON_MESG_MASK);
> > + host = pci_find_host_bridge(pdev->bus);
> > + if (!host->no_disable_sys_err)

Double negation

if (! .. ->no..

could simply be

if (host->disable_sys_err...

> > + pcie_capability_clear_word(pdev, PCI_EXP_RTCTL,
> > + SYSTEM_ERROR_INTR_ON_MESG_MASK);
>
> If I squint hard enough this sort of makes sense, but it also makes me
> confused about the normal APEI firmware-first model works.
>
> In the NON-firmare-first case, firmware isn't involved in handling AER
> errors. The Linux AER driver fields an interrupt from a Root Port,
> reads AER log registers, etc.
>
> In the normal APEI firmware-first case, when the hardware reports an
> AER event, I think firmware gets control first, and *it* reads the AER
> log registers, packages them up, and generates an interrupt to the OS,
> which reads the packaged error state from the firmware via the HEST.
>
> If I understand this special Intel VMD firmware-first case correctly,
> firmware gets control first, reads the AER log registers, and
> synthesizes what looks to the OS like a normal AER interrupt. The

Why?

Why the faking?

If firmware needs to get control, why doesn't it then *retain* control
and report the error through HEST, like others do?

AFAIUC, fw wants to do something underneath. What's wrong with making it
a normal firmware-first case?

--
Regards/Gruss,
Boris.

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