[RFC] drm/panic: Add drm panic locking

[John Ogness]

Hi Daniel,

Great to see this moving forward!

On 2024-03-01, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> But for the initial cut of a drm panic printing support I don't think
> we need that, because the critical sections are extremely small and
> only happen once per display refresh. So generally just 60 tiny locked
> sections per second, which is nothing compared to a serial console
> running a 115kbaud doing really slow mmio writes for each byte. So for
> now the raw spintrylock in drm panic notifier callback should be good
> enough.

Is there a reason you do not use the irqsave/irqrestore variants? By
leaving interrupts enabled, there is the risk that a panic from any
interrupt handler may block the drm panic handler.

John Ogness