[RFC PATCH V1 v4.10-rc3 1/1] acpi: apei: handle GSIV notification type

[Shiju Jose]

Hi James,

> -----Original Message-----
> From: James Morse [mailto:james.morse at arm.com]
> Sent: 01 March 2017 17:04
> To: Hanjun Guo; Shiju Jose
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> Gabriele Paoloni; Guohanjun (Hanjun Guo); wangxiongfeng (C); Zhengqiang
> (turing)
> Subject: Re: [RFC PATCH V1 v4.10-rc3 1/1] acpi: apei: handle GSIV
> notification type
> 
> Hi Hanjun,
> 
> On 01/03/17 08:27, Hanjun Guo wrote:
> > On 2017/2/28 21:22, James Morse wrote:
> >> On 27/02/17 18:19, Shiju Jose wrote:
> >>> Add a new GHES error source handling function for GSIV(Global
> System
> >>> Interrupt Vector).
> >>> If an error source's notification type is GSIV, then this handling
> >>> function can be registered into the GSIV handler and it can parse
> >>> and report error information when they occur.
> >>
> >> I'm missing some of the story here, but how is GSIV different from
> >> 'External Interrupt'? I'm guessing something other than the CPU
> takes this 'interrupt'...
> >
> > Yes, it's the same from CPU side (they are interrupts!), but there is
> > history behind them and the usage is different.
> >
> > I think External Interrupt was introduced before ACPI is available on
> > ARM (hardware reduced platforms), so I guess it was used for errors
> > reported to OS which were not using SCI mechanism, for example, some
> > IO error reporting.
> >
> > For External Interrupt, we don't use the ACPI event system, so for
> the
> > firmware, it just report the errors associate with the interrupt
> > number, the kernel map the interrupt number and install the irq
> > handler for it.
> >
> > For GSIV based event, it was introduced for hardware reduced platform
> > in recent ACPI revision, and ARM64 is one of its consumers. When
> > errors are reported via GSIV, ACPI event notification needs to be
> > implemented and requires the platform to define a hardware error
> > device
> > (PNP0C33) in ACPI namespace, and also a generic event device ACPI0013.
> 
> Okay, so for APEI this really means PNP0C33 was Notify()d. 'SCI' means
> the same but the route they take to get into APEI is different.
> 
> 
> > For example, if we are using SPI (ARM GIC) 100 to report errors,
> there
> > is a ACPI0013 driver in drivers/acpi/evged.c to register the irq,
> when
> 
> Aha, this is where the interrupt-magic happens.
> 
> 
> > error happened and trigger the interrupt, ACPI0013 driver will notify
> > the error device (PNP0C33), then error device driver
> > (drivers/acpi/hed.c) will process the error data form APEI table...
> 
> 
> >> The GHES GSIV code below is identical to the behaviour of the SCI
> >> Notification type... are these two names for the same thing? (I'm
> >> confused!)
> >
> > SCI is also an 'interrupt' but it's a special irq number for ACPI
> > event, and it has GPE (general purpose event) registers behind it,
> > which is used only on Intel platforms. SCI based event use
> > Method(\_GPE._L0x) to notify the error device (PNP0C33), but GSIV is
> > used for HW-reduced platform which has no GPEs.
> 
> > Hope it can clarify something :)
> 
> Yes thanks! (the mist is slowly clearing...)
> 
> If ACPI_HEST_NOTIFY_SCI and ACPI_HEST_NOTIFY_GSIV both mean 'receive
> notification from PNP0C33', is there any point having separate lists
> and add/remove functions for them?
> 
> Instead, could we rename Linux's ghes_notifier_sci() and ghes_sci list
> to describe 'hed' instead, then group the two case statements together?
> There would be no need to add a selectable CONFIG_ACPI_APEI_GSIV, as
> SCI is already built-in and this way the code added is tiny. The only
> thing we would lose is the name 'GSIV' in the not-supported error
> message which we don't need if its always supported.

This method was tested ok. However we were not sure about reusing/changing the 
existing ghes_notifier_sci() for gsiv will be accepted. 
Thus added a separate handling function ghes_notifier_gsiv() for gsiv.       

Thanks,
Shiju
> 
> 
> Thanks,
> 
> James