linux-kernel - Re: [PATCH] MIPS: smp-mt: enable all hardware interrupts on second VPE

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Date:   Thu, 7 Jul 2022 11:57:48 +0200
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Sander Vanheule <sander@...nheule.net>,
        Aleksander Jan Bajkowski <olek2@...pl>,
        martin.blumenstingl@...glemail.com, hauke@...ke-m.de,
        git@...ger-koblitz.de, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: smp-mt: enable all hardware interrupts on second
 VPE

On Wed, Jul 06, 2022 at 10:53:36AM +0100, Marc Zyngier wrote:
> On Wed, 06 Jul 2022 09:19:01 +0100,
> Thomas Bogendoerfer <tsbogend@...ha.franken.de> wrote:
> > 
> > On Wed, Jul 06, 2022 at 08:05:30AM +0100, Marc Zyngier wrote:
> > > On Sun, 03 Jul 2022 19:15:11 +0100,
> > > Sander Vanheule <sander@...nheule.net> wrote:
> > > > 
> > > > Hi Aleksander,
> > > > 
> > > > Since this is IRQ related: +CC Marc Zyngier
> > > > 
> > > > On Sat, 2022-07-02 at 21:07 +0200, Aleksander Jan Bajkowski wrote:
> > > > > This patch is needed to handle interrupts by the second VPE on
> > > > > the Lantiq xRX200, xRX300 and xRX330 SoCs. In these chips, 32 ICU
> > > > > interrupts are connected to each hardware line. The SoC supports
> > > > > a total of 160 interrupts. Currently changing smp_affinity to the
> > > > > second VPE hangs interrupts.
> > > > > 
> > > > > This problem affects multithreaded SoCs with a custom interrupt
> > > > > controller. Chips with 1004Kc core and newer use the MIPS GIC.
> > > > > 
> > > > > Also CC'ed Birger Koblitz and Sander Vanheule. Both are working
> > > > > on support for Realtek RTL930x chips with 34Kc core and Birger
> > > > > has added a patch in OpenWRT that also enables all interrupt
> > > > > lines. So it looks like this patch is useful for more SoCs.
> > > > > 
> > > > > Tested on lantiq xRX200 and xRX330.
> > > > > 
> > > > > Signed-off-by: Aleksander Jan Bajkowski <olek2@...pl>
> > > > 
> > > > Thanks for bringing up this issue. Like you say OpenWrt carries a
> > > > similar patch, and I also carry a patch on my tree to enable all CPU
> > > > IRQ lines.
> > > > 
> > > > Indiscriminately enabling all IRQ lines doesn't sit quite right with
> > > > me though, since I would expect these to be enabled
> > > > on-demand. I.e. when a peripheral requests an IRQ, or when an IRQ
> > > > controller is cascaded into one of the CPU's interrupt lines. If I
> > > > understand correctly, the IRQ mask/unmask functions in
> > > > drivers/irqchip/irq-mips-cpu.c should do this.
> > > 
> > > But this is only enabling interrupts at the CPU level, right? And the
> > > irqchip is still in control of the masking of the individual
> > > interrupts?
> > 
> > in the Lantiq case yes
> > 
> > > If both assertions are true, then this patch seems OK. If it just let
> > > any interrupt through without any control, then this is wrong.
> > > 
> > > So which one is it?
> > 
> > if there isn't an additional irqchip connected to the cpu interrupt lines,
> > this patch will cause problems.
> 
> And that's what the irq-mips-cpu driver should solve, right? In this

yes

> case, what's the problem with adopting this driver for the Lantiq
> platform (and all other ones using the same CPU)?

I guess vendor code supplied more or less the current code base and
nobody dared to change it.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]