linux-kernel - Re: [PATCH 4/5] irqchip: gic-v3: Add gic_get_irq_domain() to get the irqdomain of the GIC.

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Message-ID: <20150717074549.7a502e09@arm.com>
Date:	Fri, 17 Jul 2015 07:45:49 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	Jason Cooper <jason@...edaemon.net>,
	David Daney <david.daney@...ium.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Robert Richter <rrichter@...ium.com>,
	David Daney <ddaney.cavm@...il.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 4/5] irqchip: gic-v3: Add gic_get_irq_domain() to get
 the irqdomain of the GIC.

On Thu, 16 Jul 2015 18:32:28 +0100
Marc Zyngier <marc.zyngier@....com> wrote:

> On 16/07/15 18:14, David Daney wrote:
> > On 07/16/2015 10:09 AM, Marc Zyngier wrote:
> >> On 16/07/15 17:50, David Daney wrote:
> > [...]
> >>>> Patch 5 has established that you're using "virtual wire" SPIs, so we
> >>>> need to work on exposing that with the normal kernel abstraction, and
> >>>> not by messing with the internals of the GIC.
> >>>>
> >>>
> >>> Agreed.
> >>>
> >>> The MSI system has pci_enable_msix()/pci_disable_msix().
> >>>
> >>> I would propose something like:
> >>>
> >>> struct gic_spi_entry {
> >>> 	int spi   /* SPI number */
> >>> 	int irq;  /* kernel irq number mapped to the spi*/
> >>> 	u32 msg;  /* message to be written */
> >>> 	u64 assert_addr;
> >>> 	u64 deassert_addr;
> >>> };
> >>>
> >>> /* Fill in the SPI processing information */
> >>> int gic_map_spi(int spi, struct gic_spi_entry *data);
> >>
> >> Neither.
> >>
> >> The way to do it is to make this a *separate* IRQ domain stacked onto
> >> the SPI domain. No funky hook on the side. If it doesn't go through the
> >> normal kernel API, it doesn't reach the GIC.
> > 
> > Yes, the irqdomain does handle mapping SPI -> irq, and the message can 
> > be derived from the SPI.  However, the irqdomain infrastructure cannot 
> > supply values for either assert_addr or deassert_addr.
> 
> This is why I suggested earlier (in my reply to patch 5) that you have a
> look at the series I posted a couple of days ago to implement non-PCI
> MSI support. This would allow you to compose the domains as such:
> 
> platform-MSI -> message-SPI -> GIC
> 
> You'd end up with a msi_msg containing the GICD_SETSPI_NSR doorbell, and
> the SPI as a payload.
> 
> > Those are needed in order to use SPI.  How would you suggest that they 
> > be obtained?
> 
> Two possibilities: either you derive GICD_CLRSPI_NSR by adding 8 to the
> doorbell you got from the msi_msg structure (ugly, but limited to your
> own code), or you extend msi_msg to cater for this case.

A simpler alternative to the above would be to move all this to
firmware, and only expose a *wired* SPI to the kernel. This would have
the advantage to use the existing infrastructure for both DT and ACPI.

As a side note, that was the intended use of these registers - to
provide a "virtual wire" interface that remains mostly invisible to
software.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.
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