linux-kernel - Re: [RFC] drm/panic: Add drm panic locking

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Date: Tue, 05 Mar 2024 09:20:04 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Daniel Vetter <daniel.vetter@...ll.ch>, DRI Development
 <dri-devel@...ts.freedesktop.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Daniel Vetter
 <daniel.vetter@...ll.ch>, Daniel Vetter <daniel.vetter@...el.com>, Jocelyn
 Falempe <jfalempe@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, Lukas Wunner
 <lukas@...ner.de>, Petr Mladek <pmladek@...e.com>, Steven Rostedt
 <rostedt@...dmis.org>, Sergey Senozhatsky <senozhatsky@...omium.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David
 Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Subject: Re: [RFC] drm/panic: Add drm panic locking

Hi Daniel,

Great to see this moving forward!

On 2024-03-01, Daniel Vetter <daniel.vetter@...ll.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