[RFC/PATCH 10/16] Add a pci_irq_fixup for MSI via RTAS

[Michael Ellerman]

When RTAS is managing MSIs for us, it will/may enable MSI on devices that
support it by default. This is contrary to the Linux model where a device
is in LSI mode until the driver requests MSIs.

To remedy this we add a pci_irq_fixup call, which disables MSI if they've
been assigned by firmware and the device also supports LSI.

At the moment there is no pci_irq_fixup on pSeries, so we can just set it
unconditionally. If other platforms use the RTAS MSI backend they'll need
to check that still holds.

Signed-off-by: Michael Ellerman <michael at ellerman.id.au>
---

 drivers/pci/msi/rtas.c |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

Index: msi/drivers/pci/msi/rtas.c
===================================================================
--- msi.orig/drivers/pci/msi/rtas.c
+++ msi/drivers/pci/msi/rtas.c
@@ -238,6 +238,24 @@ static int msi_rtas_alloc(struct pci_dev
 	return -1;
 }
 
+static void msi_rtas_pci_irq_fixup(struct pci_dev *pdev)
+{
+	/* No LSI -> leave MSIs (if any) configured */
+	if (pdev->irq == NO_IRQ) {
+		msi_debug("no LSI on %s, nothing to do.\n", pci_name(pdev));
+		return;
+	}
+
+	/* No MSI -> MSIs can't have been assigned by fw, leave LSI */
+	if (check_req_msi(pdev)) {
+		msi_debug("no req#msi on %s, nothing to do.\n", pci_name(pdev));
+		return;
+	}
+
+	msi_debug("disabling existing MSI on %s\n", pci_name(pdev));
+	rtas_disable_msi(pdev);
+}
+
 static struct msi_ops rtas_msi_ops = {
 	.check = msi_rtas_check,
 	.alloc = msi_rtas_alloc,
@@ -264,5 +282,8 @@ int msi_rtas_init(void)
 
 	ppc_md.get_msi_ops = rtas_get_msi_ops;
 
+	WARN_ON(ppc_md.pci_irq_fixup);
+	ppc_md.pci_irq_fixup = msi_rtas_pci_irq_fixup;
+
 	return 0;
 }