Re: [PATCH 1/2] arm64: smp: Fix pseudo NMI issues w/ broken Mediatek FW

[Mark Rutland]

On Mon, Oct 02, 2023 at 09:45:29AM -0700, Douglas Anderson wrote:
> Some mediatek devices have the property
> "mediatek,broken-save-restore-fw" in their GIC. This means that,
> although the hardware supports pseudo-NMI, the firmware has a bug
> that blocks enabling it. When we're in this state,
> system_uses_irq_prio_masking() will return true but we'll fail to
> actually enable the IRQ in the GIC.
> 
> Let's make the code handle this. We'll detect that we failed to
> request an IPI as NMI and fallback to requesting it normally. Though
> we expect that either all of our requests will fail or all will
> succeed, it's just as cheap to keep a per-IPI bitmap and that keeps us
> robust.
> 
> Fixes: 331a1b3a836c ("arm64: smp: Add arch support for backtrace using pseudo-NMI")
> Reported-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx>
> Closes: https://issuetracker.google.com/issues/197061987#comment68
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
> 
>  arch/arm64/kernel/smp.c | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)

I'm not too keen on falling back here when we have no idea why the request failed.

I'd prefer if we could check the `supports_pseudo_nmis` static key directly to
account for the case of broken FW, e.g. as below.

Mark.

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