linux-kernel - Re: [PATCH 5/5] ARM: gic: add OF based initialization

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Date:	Sat, 17 Sep 2011 18:13:17 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Rob Herring <robherring2@...il.com>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"thomas.abraham@...aro.org" <thomas.abraham@...aro.org>,
	"jamie@...ieiles.com" <jamie@...ieiles.com>,
	"b-cousson@...com" <b-cousson@...com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH 5/5] ARM: gic: add OF based initialization

On Wed, Sep 14, 2011 at 01:51:42PM -0500, Rob Herring wrote:
> On 09/14/2011 01:34 PM, Marc Zyngier wrote:
> > Hi Rob,
> > 
> > On 14/09/11 18:57, Rob Herring wrote:
> >> Marc,
> >>
> >> On 09/14/2011 12:46 PM, Marc Zyngier wrote:
> >>> On 14/09/11 17:31, Rob Herring wrote:
> >>>> From: Rob Herring <rob.herring@...xeda.com>
> >>>>
> >>>> This adds gic initialization using device tree data. The initialization
> >>>> functions are intended to be called by a generic OF interrupt
> >>>> controller parsing function once the right pieces are in place.
> >>>>
> >>>> PPIs are handled using 3rd cell of interrupts properties to specify the cpu
> >>>> mask the PPI is assigned to.
> >>>>
> >>>> Signed-off-by: Rob Herring <rob.herring@...xeda.com>
> >>>> ---
> >>>>  Documentation/devicetree/bindings/arm/gic.txt |   53 ++++++++++++++++++++++++
> >>>>  arch/arm/common/gic.c                         |   55 +++++++++++++++++++++++--
> >>>>  arch/arm/include/asm/hardware/gic.h           |   10 +++++
> >>>>  3 files changed, 114 insertions(+), 4 deletions(-)
> >>>>  create mode 100644 Documentation/devicetree/bindings/arm/gic.txt
> >>>>
> >>>> diff --git a/Documentation/devicetree/bindings/arm/gic.txt b/Documentation/devicetree/bindings/arm/gic.txt
> >>>> new file mode 100644
> >>>> index 0000000..6c513de
> >>>> --- /dev/null
> >>>> +++ b/Documentation/devicetree/bindings/arm/gic.txt
> >>>> @@ -0,0 +1,53 @@
> >>>> +* ARM Generic Interrupt Controller
> >>>> +
> >>>> +ARM SMP cores are often associated with a GIC, providing per processor
> >>>> +interrupts (PPI), shared processor interrupts (SPI) and software
> >>>> +generated interrupts (SGI).
> >>>> +
> >>>> +Primary GIC is attached directly to the CPU and typically has PPIs and SGIs.
> >>>> +Secondary GICs are cascaded into the upward interrupt controller and do not
> >>>> +have PPIs or SGIs.
> >>>> +
> >>>> +Main node required properties:
> >>>> +
> >>>> +- compatible : should be one of:
> >>>> +	"arm,cortex-a9-gic"
> >>>> +	"arm,arm11mp-gic"
> >>>> +- interrupt-controller : Identifies the node as an interrupt controller
> >>>> +- #interrupt-cells : Specifies the number of cells needed to encode an
> >>>> +  interrupt source.  The type shall be a <u32> and the value shall be 3.
> >>>> +
> >>>> +  The 1st cell is the interrupt number. 0-15 are reserved for SGIs. 16-31 are
> >>>> +  for PPIs.
> >>>> +
> >>>> +  The 2nd cell is the level-sense information, encoded as follows:
> >>>> +                    1 = low-to-high edge triggered
> >>>> +                    2 = high-to-low edge triggered
> >>>> +                    4 = active high level-sensitive
> >>>> +                    8 = active low level-sensitive
> >>>> +
> >>>> +  Only values of 1 and 4 are valid for GIC 1.0 spec.
> >>>> +
> >>>> +  The 3rd cell contains the mask of the cpu number for the interrupt source.
> >>>> +  The cpu mask is only valid for PPIs and shall be 0 for SPIs. This value shall
> >>>> +  be 0 for PPIs.
> >>>      ^^^^^^^^^^^^^
> >>>
> >>> Typo here ? The way I understand it, it should read "For PPIs, this
> >>> value shall be the mask of the possible CPU numbers for the interrupt
> >>> source" (or something to similar effect...).
> >>>
> >>
> >> Cut and paste error. This sentence goes in the previous paragraph. What
> >> I meant is the 2nd cell should contain 0 for PPIs as you cannot set the
> >> edge/level on PPIs (that is always true, right?). I probably should also
> >> add 0 in the list of values.
> > 
> > Ah, right. It makes sense indeed. You're correct about PPIs polarity,
> > this is defined by the hardware and cannot be configured. But it may be
> > interesting to have the DT to reflect the way the hardware is actually
> > configured (on the Cortex-A9, some PPIs are configured active-low, and
> > others are rising-edge).
> 
> So we should allow specifying what it is as the OS may need to know that.

If it is a difference between level & edge, then the OS absolutely
needs to know about it.

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