FAILED: patch "[PATCH] PCI/MSI: Add an option to write MSIX ENTRY_DATA before any" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x cf761e3dacc6ad5f65a4886d00da1f9681e6805a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025042119-tried-strenuous-da3e@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From cf761e3dacc6ad5f65a4886d00da1f9681e6805a Mon Sep 17 00:00:00 2001
From: Jonathan Currier <[email protected]>
Date: Sun, 17 Nov 2024 17:48:42 -0600
Subject: [PATCH] PCI/MSI: Add an option to write MSIX ENTRY_DATA before any
reads

Commit 7d5ec3d36123 ("PCI/MSI: Mask all unused MSI-X entries") introduced a readl() from ENTRY_VECTOR_CTRL before the writel() to ENTRY_DATA.

This is correct, however some hardware, like the Sun Neptune chips, the NIU module, will cause an error and/or fatal trap if any MSIX table entry is read before the corresponding ENTRY_DATA field is written to.

Add an optional early writel() in msix_prepare_msi_desc().

index 6569ba3577fe..8b8848788618 100644
@@ -615,6 +615,9 @@ void msix_prepare_msi_desc(struct pci_dev *dev, struct msi_desc *desc)
 		void __iomem *addr = pci_msix_desc_addr(desc);
 
 		desc->pci.msi_attrib.can_mask = 1;
+		/* Workaround for SUN NIU insanity, which requires write before read */
+		if (dev->dev_flags & PCI_DEV_FLAGS_MSIX_TOUCH_ENTRY_DATA_FIRST)
+			writel(0, addr + PCI_MSIX_ENTRY_DATA);
 		desc->pci.msix_ctrl = readl(addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
 	}
 }

index 0e8e3fd77e96..51e2bd6405cd 100644
@@ -245,6 +245,8 @@ enum pci_dev_flags {
 	PCI_DEV_FLAGS_NO_RELAXED_ORDERING = (__force pci_dev_flags_t) (1 << 11),
 	/* Device does honor MSI masking despite saying otherwise */
 	PCI_DEV_FLAGS_HAS_MSI_MASKING = (__force pci_dev_flags_t) (1 << 12),
+	/* Device requires write to PCI_MSIX_ENTRY_DATA before any MSIX reads */
+	PCI_DEV_FLAGS_MSIX_TOUCH_ENTRY_DATA_FIRST = (__force pci_dev_flags_t) (1 << 13),
 };
 
 enum pci_irq_reroute_variant {