On 10/23/21 2:36 PM, Vladimir Murzin wrote:

On 10/23/21 2:18 PM, Marc Zyngier wrote:

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On Sat, 23 Oct 2021 13:06:25 +0100,
Vladimir Murzin [off-list ref] wrote:

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On 10/22/21 7:43 PM, Marc Zyngier wrote:

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On Fri, 22 Oct 2021 18:58:54 +0100,
Mark Rutland [off-list ref] wrote:

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On Fri, Oct 22, 2021 at 05:34:20PM +0100, Vladimir Murzin wrote:

[...]

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As for TODO, is [1] look something you have been thinking of? IIUC,
the show stopper is that hwirq is being passed from exception entry
which retrieved via xPSR (IPSR to be precise). OTOH hwirq also available
via Interrupt Controller Status Register (ICSR) thus can be used in
driver itself... I gave [1] a go and it runs fine, yet I admit I might
be missing something...

I hadn't thought about it in much detail, but that looks good!

I was wondering if we needed something like a
handle_arch_vectored_irq(), but if we can rely on the ICSR that seems
simpler overall. I'm not at all familiar with M-class, so I'm not sure
if there are pitfalls in this area.

Why can't we just use IPSR instead from the C code? It has the
potential of being of lower latency then a MMIO read (though I have no
idea whether it makes a material difference on M-class) and from what
I can see in the arch spec, they are strictly equivalent.

Hmmm, less arch specific asm(s) in driver code, no?

Well, it isn't like this driver is going to be useful on anything
else, is it?

Well, with some work to unwire it from arch/arm it can be COMPILE_TEST :)

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If there is no overhead in reading from MMIO compared to the
architected register, then I agree that ICSR is the way to
go. Is there any chance you could measure it on a HW platform? Or
maybe in emulation?

My MPS{2,3} boards left in office and I'm on holiday next week... OTOH, I
have no strong opinion on ICSR vs IPSR, I just wanted to check how much
work it'd be to close TODO per my (quite limited) understanding :)

One month and a week later... 

I observe that in terms of performance

   MRS       r0, ipsr

is equivalent to readl_relaxed(BASEADDR_V7M_SCB + V7M_SCB_ICSR)

   MOV.W   r3, #3758153728
   LDR.W   r0, [r3, #3332]

Old compilers can produce less performant sequence like

   LDR      r3,0xbcc0
   ADD.W    r3,r3,#0xaf00
   LDR      r0,[r3,#0]

So, what would be your preference?

Cheers
Vladimir

Cheers
Vladimir

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Thanks,

	M.

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