linux-kernel - Re: [PATCH] thunderbolt: Return -ENOTSUPP when cm

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Message-ID: <20251204101116.GA1613537@black.igk.intel.com>
Date: Thu, 4 Dec 2025 11:11:16 +0100
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: Haotian Zhang <vulab@...as.ac.cn>
Cc: andreas.noever@...il.com, westeri@...nel.org, YehezkelShB@...il.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thunderbolt: Return -ENOTSUPP when cm_ops callbacks are
 missing

Hi,

On Thu, Dec 04, 2025 at 05:32:24PM +0800, Haotian Zhang wrote:
> Several tb_domain* helpers return -EPERM when the corresponding cm_ops
> callback is NULL. A NULL callback indicates the operation is not
> supported by the connection manager, not a permission denial.

These specifically return -EPERM on purpose because these are used when
PCIe tunnel is established and torn down. If the connection manager
implementation does not provide them it means you don't have permission to
deal with the PCIe tunnels.