linux-kernel - [PATCH] PCI: vmd: Remove MSI-X check on child devices

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Message-Id: <20250811053935.4049211-1-namcao@linutronix.de>
Date: Mon, 11 Aug 2025 07:39:35 +0200
From: Nam Cao <namcao@...utronix.de>
To: Nirmal Patel <nirmal.patel@...ux.intel.com>,
	Jonathan Derrick <jonathan.derrick@...ux.dev>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Nam Cao <namcao@...utronix.de>,
	Ammar Faizi <ammarfaizi2@...weeb.org>
Subject: [PATCH] PCI: vmd: Remove MSI-X check on child devices

Commit d7d8ab87e3e7 ("PCI: vmd: Switch to msi_create_parent_irq_domain()")
added a WARN_ON sanity check that child devices support MSI-X, because VMD
document says [1]:

    "Intel VMD only supports MSIx Interrupts from child devices and
    therefore the BIOS must enable PCIe Hot Plug and MSIx interrups [sic]."

However, on Ammar's machine, a PCIe port below VMD does not support MSI-X,
triggering this WARN_ON.

This inconsistency between the document and reality should be investigated
further. For now, remove the MSI-X check.

Allowing child devices without MSI-X despite what the document says does
sound suspicious, but that's what the driver had been doing before the
WARN_ON is added.

Fixes: d7d8ab87e3e7 ("PCI: vmd: Switch to msi_create_parent_irq_domain()")
Link: https://cdrdv2-public.intel.com/776857/VMD_White_Paper.pdf [1]
Reported-by: Ammar Faizi <ammarfaizi2@...weeb.org>
Closes: https://lore.kernel.org/linux-pci/aJXYhfc%2F6DfcqfqF@linux.gnuweeb.org/
Tested-by: Ammar Faizi <ammarfaizi2@...weeb.org>
Signed-off-by: Nam Cao <namcao@...utronix.de>
---
 drivers/pci/controller/vmd.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index b679c7f28f51..1bd5bf4a6097 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -306,9 +306,6 @@ static bool vmd_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
 				  struct irq_domain *real_parent,
 				  struct msi_domain_info *info)
 {
-	if (WARN_ON_ONCE(info->bus_token != DOMAIN_BUS_PCI_DEVICE_MSIX))
-		return false;
-
 	if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
 		return false;
 
-- 
2.39.5