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Date: Sat, 2 May 2026 21:47:17 +0200
From: Lukas Wunner <lukas@wunner.de>
To: Icenowy Zheng <zhengxingda@iscas.ac.cn>
Cc: Manivannan Sadhasivam <mani@kernel.org>, Han Gao <gaohan@iscas.ac.cn>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= <u.kleine-koenig@baylibre.com>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	Ilpo =?iso-8859-1?Q?J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>,
	Kees Cook <kees@kernel.org>, Chen Wang <unicorn_wang@outlook.com>,
	linux-pci@vger.kernel.org, sophgo@lists.linux.dev,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	Han Gao <rabenda.cn@gmail.com>, Inochi Amaoto <inochiama@gmail.com>,
	Vivian Wang <wangruikang@iscas.ac.cn>, Yao Zi <me@ziyao.cc>,
	stable@vger.kernel.org
Subject: Re: [PATCH 2/2] PCI: Add quirk to disable PCIe port services on
 Sophgo SG2042
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References: <20260331175658.1015829-1-gaohan@iscas.ac.cn>
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In-Reply-To: <0f42afefd9322779af5463b696c55b08d2296ea8.camel@iscas.ac.cn>

On Sat, May 02, 2026 at 09:58:04PM +0800, Icenowy Zheng wrote:
> The problem is that the MSI controller has only 16 MSIs usable (it's
> wrongly described as 32 previously, a fix to this is pending[1]), and
> the failing device have an onboard PCIe switch, which created many PCIe
> ports (and corresponding pcieport devices).

Is the SG2042 only used in that single product?  If it is used in other
products which do not have an on-board PCIe switch, why do you want to
disable MSIs on those other products as well?

My point is, you want to constrain this to a specific product, not to
the SoC.  Can you maybe solve this by not specifying interrupts in the
devicetree for the PCIe switch?

> With pcieport devices activated, 11 MSIs are requested by the pcieport
> drivers -- 3 SoC PCIe ports and 8 switch downstream ports. Then only 5
> MSIs are available, but there're still 10 downstream-facing PCIe ports
> now (and 5 of them are hardwired to onboard peripherals).

pcieport can make do with a single MSI vector because all port services
support a shared interrupt.  But I assume your point is that this
particular product has so many PCIe ports that you're still close
to the 16 MSIs limit?

Thanks,

Lukas