Re: IDE DVD and CD drive seem to not work with Linux desktop 3.3.0-030300-generic

[Matthew Garrett <mjg59@srcf.ucam.org>]

Ok, this is very odd - ASPM is disabled in both cases. The only thing I 
can think of here is that the hardware dislikes us writing to the 
registers? Can you test this patch on top of the broken kernel?

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 24f049e..04eb680 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -185,6 +185,7 @@ static void pcie_aspm_configure_common_clock(struct pcie_link_state *link)
 	int ppos, cpos, same_clock = 1;
 	u16 reg16, parent_reg, child_reg[8];
 	unsigned long start_jiffies;
+	bool retrain = false;
 	struct pci_dev *child, *parent = link->pdev;
 	struct pci_bus *linkbus = parent->subordinate;
 	/*
@@ -215,7 +216,10 @@ static void pcie_aspm_configure_common_clock(struct pcie_link_state *link)
 			reg16 |= PCI_EXP_LNKCTL_CCC;
 		else
 			reg16 &= ~PCI_EXP_LNKCTL_CCC;
-		pci_write_config_word(child, cpos + PCI_EXP_LNKCTL, reg16);
+		if (reg16 != child_reg[PCI_FUNC(child->devfn)]) {
+			retrain = true;
+			pci_write_config_word(child, cpos + PCI_EXP_LNKCTL, reg16);
+		}
 	}
 
 	/* Configure upstream component */
@@ -225,9 +229,15 @@ static void pcie_aspm_configure_common_clock(struct pcie_link_state *link)
 		reg16 |= PCI_EXP_LNKCTL_CCC;
 	else
 		reg16 &= ~PCI_EXP_LNKCTL_CCC;
-	pci_write_config_word(parent, ppos + PCI_EXP_LNKCTL, reg16);
+	if (reg16 != parent_reg) {
+		retrain = true;
+		pci_write_config_word(parent, ppos + PCI_EXP_LNKCTL, reg16);
+	}
 
 	/* Retrain link */
+	if (!retrain)
+		return;
+
 	reg16 |= PCI_EXP_LNKCTL_RL;
 	pci_write_config_word(parent, ppos + PCI_EXP_LNKCTL, reg16);
 
@@ -436,13 +446,16 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 
 static void pcie_config_aspm_dev(struct pci_dev *pdev, u32 val)
 {
-	u16 reg16;
+	u16 reg16, orig_reg16;
 	int pos = pci_pcie_cap(pdev);
 
 	pci_read_config_word(pdev, pos + PCI_EXP_LNKCTL, &reg16);
+	orig_reg16 = reg16;
 	reg16 &= ~0x3;
 	reg16 |= val;
-	pci_write_config_word(pdev, pos + PCI_EXP_LNKCTL, reg16);
+
+	if (reg16 != orig_reg16)
+		pci_write_config_word(pdev, pos + PCI_EXP_LNKCTL, reg16);
 }
 
 static void pcie_config_aspm_link(struct pcie_link_state *link, u32 state)

-- 
Matthew Garrett | mjg59@srcf.ucam.org