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Subject: Re: [PATCH 2/6] bcma: mips: explicit assign IRQ numbers
From: Nathan Hintz <nlhintz@hotmail.com>
To: Hauke Mehrtens <hauke@hauke-m.de>
CC: =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <zajec5@gmail.com>,
	linville@tuxdriver.com, linux-wireless@vger.kernel.org
Date: Sun, 6 Jan 2013 18:10:23 -0800
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On Sun, 2013-01-06 at 21:35 +0100, Hauke Mehrtens wrote:
> On 01/04/2013 08:43 AM, Rafał Miłecki wrote:
> > 2013/1/4 Hauke Mehrtens <hauke@hauke-m.de>:
> >> The assignment of the IRQs to the cores of the chips by iterating over
> >> the cores is complicated and causes problems with SoC like the BCM4706
> >> with two GMAC core where just one should get a dedicated IRQ number.
> > 
> > Well, the only problem on BCM4706 is that second (broken/dangling)
> > GMAC core gets it's own IRQ. With such a "waste" of one IRQ line we
> > may end up using shared IRQ for some other core like PCIE/USB.
> > This issue can be simply workarounded (with 2 LOC) and sounds sane:
> > bug in HW, specific workaround in a driver. We already have similar
> > workarounds for other "dangling" cores.
> > 
> > I don't know about any other issues with BCM4706 IRQs.
> > 
> > Are there any other (more serious?) issues on different SoCs? Any
> > advantages of hardcoding IRQs (per chipset) rather than keeping this
> > simple algorithm? Do the IRQ lines differ? Is this somehow better to
> > use (just an example) IRQ 3 instead of IRQ 4 for GMAC core?
> 
> Normally the boot loader (CFE) assigns IRQs to the cores on the bus. The
> old code mostly worked because CFE did it correct most of the time.
> 
> On my bcm4718 the I2S core (id 0x834) does not get any IRQ from CFE, but
> at least Nathan (nlhintz) wants to assign an IRQ (shared) to this core.
This is the way it is in the Broadcom SDK; whether it matters or not, I
don't know.  It seemed to be working without it too.  How would one tell
if it is important?
> 
> It is also possible to extend the algorithm to solve all these things,
> but I think the new code is better to understand.
> 
> I do not think that there will be any new SoC using bcma and a mips cpu,
> I haven't seen an announcement for such a SoC at the Broadcom web page,
> just arm based devices, so I assume this list is complete.
> 
> Hauke
> 

Nathan