linux-kernel - Re: [PATCH] nouveau: pci: quiesce GPU on shutdown

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Message-Id: <DFTV9NQTFFU0.NOD8PPU8HW8L@kernel.org>
Date: Wed, 21 Jan 2026 02:12:56 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Li Chen" <me@...ux.beauty>
Cc: "Dave Airlie" <airlied@...il.com>, "Lyude Paul" <lyude@...hat.com>,
 "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard"
 <mripard@...nel.org>, "Thomas Zimmermann" <tzimmermann@...e.de>, "Simona
 Vetter" <simona@...ll.ch>, "dri-devel" <dri-devel@...ts.freedesktop.org>,
 "nouveau" <nouveau@...ts.freedesktop.org>, "linux-kernel"
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nouveau: pci: quiesce GPU on shutdown

On Wed Jan 21, 2026 at 1:50 AM CET, Li Chen wrote:
>  > > +       usleep_range(200, 400);\
>  > 
>  > Why is this needed? it at least needs a comment.
>
> This patch is needed for kexec/KHO/LUO reboot: firmware reset is skipped, so the GPU may remain in an active/DMA 
> state and the next kernel can fail to re-init nouveau. We can’t call the full DRM/TTM teardown from ->shutdown() because
> userspace may still hold DRM fds during shutdown, which triggers WARNs.
>
> So the shutdown hook reuses the suspend/quiesce path (safe with open fds) and then powers down the PCI function (D3hot)
> to leave the device in a consistent state for the next kernel.

I think the question was about the usleep_range() specifically. :)