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Date: Fri, 25 Sep 2026 20:49:26 +0200
From: Lukas Wunner <lukas@wunner.de>
To: Zhu Qiyu <qiyuzhu2@amd.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] PCI: pciehp: Avoid dropping hotplug interrupts due to
 stale HPIE
Message-ID: <arbCNu_Ozv2j_CEv@wunner.de>
References: <20260924101929.143806-1-qiyuzhu2@amd.com>
 <20260925114635.192878-1-qiyuzhu2@amd.com>
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In-Reply-To: <20260925114635.192878-1-qiyuzhu2@amd.com>

On Fri, Sep 25, 2026 at 11:46:35AM +0000, Zhu Qiyu wrote:
> pciehp_isr() uses the Hot-Plug Interrupt Enable (HPIE) bit in
> ctrl->slot_ctrl to reject interrupts when hotplug interrupts are
> disabled.  This check is needed because hotplug can share an interrupt
> with other sources, including native PME.
> 
> However, ctrl->slot_ctrl is updated from hardware on every Slot Control
> Register read-modify-write.  A firmware change to HPIE can race with an
> unrelated driver operation, such as an LED indicator update:

Firmware is not allowed to change the Slot Control Register once it has
granted control of PCI Express Native Hot Plug Control to the operating
system.

>From PCIe r3.3 table 4-6 bit 0:

   "Additionally, after control is transferred to the operating system,
    firmware must not update the state of hot plug slots, including the
    state of the indicators and power controller."

Are you seeing this on a real-world system or is it an LLM-generated
hallucination?

If the former, please consider fixing this through a firmware update.

Thanks,

Lukas