linux-kernel - Re: [PATCH V3 06/11] irqchip: bcm7120-l2: Change DT binding to allow non-contiguous IRQEN/IRQSTAT

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Date:	Wed, 26 Nov 2014 21:13:15 +0100
From:	Jonas Gorski <jogo@...nwrt.org>
To:	Kevin Cernekee <cernekee@...il.com>
Cc:	Ralf Baechle <ralf@...ux-mips.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jon Fraser <jfraser@...adcom.com>,
	Dmitry Torokhov <dtor@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>,
	Brian Norris <computersforpeace@...il.com>,
	MIPS Mailing List <linux-mips@...ux-mips.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 06/11] irqchip: bcm7120-l2: Change DT binding to allow
 non-contiguous IRQEN/IRQSTAT

On Wed, Nov 26, 2014 at 7:54 PM, Kevin Cernekee <cernekee@...il.com> wrote:
> On Wed, Nov 26, 2014 at 2:25 AM, Jonas Gorski <jogo@...nwrt.org> wrote:
>> On Wed, Nov 26, 2014 at 10:45 AM, Jonas Gorski <jogo@...nwrt.org> wrote:
>>> As far as I can see, we have three distinct layouts here:
>>>
>>> a) An arbitrary number of 32-bit Mask/Status-pairs (3384/6838). No per
>>> thread support (well, not sure about 60333).
>>>
>>> b) An arbitrary length (32 to 128 bit) Mask register, followed by a
>>> same length Status register (63xx except 63381, 6818, 6828); repeated
>>> for each thread.
>>>
>>> c) A single arbitrary length (currently only 128 bit) Status register,
>>> followed by per thread same length Mask registers (63381).
>>>
>>> On a first glance this could translate to three distinct
>>> drivers/compatible properties, where each expects different reg = <>;
>>> contents.
>>>
>>> For a), it should be enough to expand the current 7120-l2 driver to
>>> accept/use more than one 0x8 length register, which should simplify
>>> the register map setup.
>>>
>>> For b) we could add a a new compatible name (maybe bcm6358-l2, because
>>> that was AFAICT the first one with blocks) that will use the 8 to 32
>>> byte length regs (one for each block). For now we could ignore the SMP
>>> capability of it and make it a variant of the 7120-l2 driver, and when
>>> we add SMP support, split it into a second different driver if we want
>>> to avoid having all the spinlock for register accesses even for a).
>>>
>>> We could then even easily document/add the extra block registers /
>>> interrrupts in documentation / the dtsi files before actually
>>> supporting them, because we only have a fixed amount of regs/irqs to
>>> expect in the !SMP case and can easily ignore the extra
>>> registers/interrupts.
>>>
>>> For c) we could add a a third compatible name (bcm63381-l2), also with
>>> its own setup routine. I would guess it doesn't matter if both
>>> thread's irqstatus register pointers point to the same region.
>>
>> This split-up is especially tempting to me after I had a closer look
>> at the current 7120-l2 driver, which already accepts more than one
>> interrupt, but uses it in a different way. So even if we try to make
>> it very flexible with only one compatible property,
>>
>>    reg = <irqstatus0 irqmask0 irqstatus1 irqmask1>;
>>    interrupts = <irq0>, <irq1>;
>>
>> Could then mean either irq0 is for interrupts 0..31 (mask/status0) and
>> irq1 for interrupts 32 .. 64 (mask/status1), or irq0 is for interrupts
>> 0..31 on cpu0, and irq1 is for interrupts 0..31 on cpu1, and then
>> would require an additional property to tell them apart, for which we
>> then also could just use a different compatible name, and have (IMHO)
>> a lot less headache.  (I wonder why we couldn't just have had more
>> than one instance of 7120-l2 in the dts for the first case)
>
> I don't think we've used this driver to implement the first case yet.
>
> The initial use of the driver was for the BCM7xxx IRQ0 block, which is
> wired up according to the ASCII art diagram in
> Documentation/devicetree/bindings/interrupt-controller/brcm,bcm7120-l2-intc.txt
> .  i.e. different sets of bits in a single irqstatus0/irqmask0 pair
> map to different parent IRQs.  The bits handled by each parent IRQ are
> indicated in the brcm,int-map-mask property.
>
> And now on BCM3384, of course, we're seeing the output from two 32-bit
> irqstatus/irqmask words ORed together into a single parent IRQ, for
> periph_intc.  The other instances do have their own DT nodes.

Ah indeed, I read it wrong. But it still the same "problem" of regs +
> 1 parent interrupts already having a different meaning for bcm7120
than what they will have for bcm63xx.

I just successfully* booted bcm63xx with my proposed changes to
bcm7120-l2-intc with a hacked together bcm6358-l2-intc probe routine,
and I now think even less that having these two in one driver merged
is a good idea. Especially if we want to support the affinity stuff.
There seems to be quite a bit that will need to be changed for it.


Jonas

* took me a while to find your OF_DECLARE_2() for the mips-intc - sneaky ;p.

P.S: I wonder how this patchset is supposed to go, as it depends on
earlier bcm7120/generic irqchip patches marked in patchwork as "other
subsystem".
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