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Date:   Mon, 16 Jan 2017 15:24:13 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Hanjun Guo <guohanjun@...wei.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Hanjun Guo <hanjun.guo@...aro.org>, huxinwei@...wei.com,
        Kefeng Wang <wangkefeng.wang@...wei.com>, yimin@...wei.com,
        Jon Masters <jcm@...hat.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com,
        Sinan Kaya <okaya@...eaurora.org>, linux-acpi@...r.kernel.org,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Matthias Brugger <mbrugger@...e.com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Agustin Vega-Frias <agustinv@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, Ma Jun <majun258@...wei.com>
Subject: Re: [PATCH v7 15/15] irqchip: mbigen: Add ACPI support

On Mon, Jan 16, 2017 at 10:23:16PM +0800, Hanjun Guo wrote:
> Hi Lorenzo,
> 
> On 2017/1/16 19:38, Lorenzo Pieralisi wrote:
> > On Sat, Jan 14, 2017 at 10:56:54AM +0800, Hanjun Guo wrote:
> >> Hi Lorenzo,
> >>
> >> On 2017/1/13 18:21, Lorenzo Pieralisi wrote:
> >>> On Wed, Jan 11, 2017 at 11:06:39PM +0800, Hanjun Guo wrote:
> >>>> With the preparation of platform msi support and interrupt producer
> >>>> in DSDT, we can add mbigen ACPI support now.
> >>>>
> >>>> We are using _PRS methd to indicate number of irq pins instead
> >>>> of num_pins in DT to avoid _DSD usage in this case.
> >>>>
> >>>> For mbi-gen,
> >>>>     Device(MBI0) {
> >>>>           Name(_HID, "HISI0152")
> >>>>           Name(_UID, Zero)
> >>>>           Name(_CRS, ResourceTemplate() {
> >>>>                   Memory32Fixed(ReadWrite, 0xa0080000, 0x10000)
> >>>>           })
> >>>>
> >>>>           Name (_PRS, ResourceTemplate() {
> >>>> 		  Interrupt(ResourceProducer,...) {12,14,....}
> >>> I still do not understand why you are using _PRS for this, I think
> >>> the MBIgen configuration is static and if it is so the Interrupt
> >>> resource should be part of the _CRS unless there is something I am
> >>> missing here.
> >> Sorry for not clear in the commit message. MBIgen is an interrupt producer
> >> which produces irq resource to devices connecting to it, and MBIgen itself
> >> don't consume wired interrupts.
> > That's why you mark it as ResourceProducer, but that's not a reason to
> > put it in the _PRS instead of _CRS.
> 
> If using _CRS for the interrupt resource, the irq number represented
> will be mapped (i.e acpi_register_gsi()), then will conflict with the
> irq number of devices consuming it (mbigen is producing the
> interrupts), but I agree with you that let's ask Rafael's point of
> view.

Aha ! So here is why you are using _PRS because the kernel turns _CRS
Interrupt resources (even producers) into GSIs which is probably a
kernel bug, is that the reason ?

We don't abuse firmware bindings to make the kernel work, that's _never_
a good idea.

If the interrupt resource is a Resource Producer core ACPI should not
register the IRQ because that's not a GSI, probably this should be part of
Agustin changes too ?

> > IIUC _PRS is there to provide a way to define the possible resource
> > settings of a _configurable_ device (ie programmable) so that the actual
> > resource value you would programme with a call to its _SRS is sane (ie
> > the OS has a way, through the _PRS, to detect what possible resource
> > settings are available for the device).
> >
> > I think Rafael has more insights into how the _PRS is used on x86
> > systems so I would ask his point of view here before merrily merging
> > this code.
> 
> OK, Rafael is traveling now, hope he will have time to take a look.
> 
> How about updating this patch set then sending a new version for review
> with this patch unchanged? if Rafael have comments on this one, I will
> send a single updated one for this patch (if no other changes).

I think this patch (and the FW that goes with it) is wrong, but the rest
of the series, in particular the IORT bits, are ok with me.

Lorenzo

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