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AMD760MPX: bogus chispset ? (was PROBLEM: sound is stutter, sizzle with lasts kernel releases)

DISCUSSION Alan Cox 2 participants 5 messages Jul 11, 2003 – Jul 13, 2003 1 message not in the archive

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Alan Cox

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#1 lore raw
Quoted 4 lines · xi

Now I have done some investigations, and I think I have found the
problem: It has appeared between kernel-2.4.18-pre9 and kernel-2.4.18-rc1 If I am not wrong, between these two versions, Alan Cox did a change in drivers/pci/quirks.c and this is this change which cause the problem.

As I read the documentation the other change is also required in this situation to avoid a chipset lockup. It might be worth you rechecking the AMD errata docs for 762/768 again to be sure I didnt screw up and there are not newer rules for other revisions.

#2 lore raw
Quoted 11 lines · Alan Cox
Quoted 2 lines · xi

Now I have done some investigations, and I think I have found the problem: It has appeared between kernel-2.4.18-pre9 and kernel-2.4.18-rc1 If I am not wrong, between these two versions, Alan Cox did a change in drivers/pci/quirks.c and this is this change which cause the problem.

As I read the documentation the other change is also required in this situation to avoid a chipset lockup. It might be worth you rechecking the AMD errata docs for 762/768 again to be sure I didnt screw up and there are not newer rules for other revisions.

Ok, I have rechecked the errata docs. I have not found any recommandation change for PCI compliance configuration registers.

And one interesting thing:
in the AMD762 datasheet (24462.pdf) page 231 (Recommanded BIOS settings), I can see this: "Numerical Values shown with h or b are preferred settings." ; and AMD recommand this:
-> set bits 2 and 1 of register 0x4C to "0b"
-> set bits 23 and 3 respectively to "0b" and "1b"

I can confirm that these settings works much more better, even if they don't exactly follow PCI specs. And I don't think this is specific to my
cards since I have tested others.
Furthermore, my AMD762 is revision B1 (just before the last one: C0), and my AMD768 revision is B2, the last one.

Would you accept I make a patch which doesn't make any change in these registers at least up to AMD762 revision B1 (ie keeping recommanded values from AMD) ? Or could you propose an other solution ?

Regards,
Xavier

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Homepage:
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author
#3 lore raw
Quoted 13 lines · xi

And one interesting thing:
in the AMD762 datasheet (24462.pdf) page 231 (Recommanded BIOS settings), I can see this: "Numerical Values shown with h or b are preferred settings." ; and AMD recommand this:
-> set bits 2 and 1 of register 0x4C to "0b"
-> set bits 23 and 3 respectively to "0b" and "1b"

I can confirm that these settings works much more better, even if they don't exactly follow PCI specs. And I don't think this is specific to my
cards since I have tested others.
Furthermore, my AMD762 is revision B1 (just before the last one: C0), and my AMD768 revision is B2, the last one.

Quoted 3 lines

Would you accept I make a patch which doesn't make any change in these registers at least up to AMD762 revision B1 (ie keeping recommanded values from AMD) ?

Lets try the AMD recommended settings. My old doc doesnt seem to have those. I'll by happy to trial the patch in -ac and see if it plays up the usual suspects for PCI spec violations (tg3 and i2o)

#4 lore raw
Quoted 11 lines · Alan Cox
Quoted 9 lines · xi

And one interesting thing:
in the AMD762 datasheet (24462.pdf) page 231 (Recommanded BIOS settings), I can see this: "Numerical Values shown with h or b are preferred settings." ; and AMD recommand this:
-> set bits 2 and 1 of register 0x4C to "0b"
-> set bits 23 and 3 respectively to "0b" and "1b"

I can confirm that these settings works much more better, even if they don't exactly follow PCI specs. And I don't think this is specific to my
cards since I have tested others.
Furthermore, my AMD762 is revision B1 (just before the last one: C0), and my AMD768 revision is B2, the last one.

Quoted 7 lines
Quoted 1 line

Would you accept I make a patch which doesn't make any change in these registers at least up to AMD762 revision B1 (ie keeping recommanded values from AMD) ?

Lets try the AMD recommended settings. My old doc doesnt seem to have those. I'll by happy to trial the patch in -ac and see if it plays up the usual suspects for PCI spec violations (tg3 and i2o)

Ok, I provide two patchs with different behaviour:

* patch_AMD762_PCI_compliance_set_by_bios.diff : lets the BIOS decide about PCI configuration

* patch_AMD762_PCI_default_AMD_settings.diff : follow AMD recommendations but not PCI specs.

Patch are against drivers/pci/quirks.c from 2.4.22-pre4

Regards,
Xavier

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E-mail:
[email protected] [email protected]
Please no longer use [email protected], this e-mail will be removed soon.

Homepage:
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quirks.c renamed from quirks_original.c +12 -11
@@ -464,22 +464,23 @@
  * Following the PCI ordering rules is optional on the AMD762. I'm not
  * sure what the designers were smoking but let's not inhale...
  *
- * To be fair to AMD, it follows the spec by default, its BIOS people
- * who turn it off!
+ * In fact, AMD even recommends to don't follow PCI standards
+ * in the section "Recommended BIOS settings" of the datasheet
  */
  
 static void __init quirk_amd_ordering(struct pci_dev *dev)
 {
-	u32 pcic;
-	pci_read_config_dword(dev, 0x4C, &pcic);
-	if((pcic&6)!=6)
+	u32 pcic1,pcic2;
+
+	pci_read_config_dword(dev, 0x4C, &pcic1);
+	pci_read_config_dword(dev, 0x84, &pcic2);
+
+	if((pcic1&6)!=6 || (pcic2&(1<<23))!=(1<<23))
 	{
-		pcic |= 6;
-		printk(KERN_WARNING "BIOS failed to enable PCI standards compliance, fixing this error.\n");
-		pci_write_config_dword(dev, 0x4C, pcic);
-		pci_read_config_dword(dev, 0x84, &pcic);
-		pcic |= (1<<23);	/* Required in this mode */
-		pci_write_config_dword(dev, 0x84, pcic);
+		/* The AMD762 doesn't follow PCI standards, but it seems to work better in this mode !
+		   In order to be fully PCI standards compliant, we should :
+		   set bit 1 and 2 of register 0x4C ; set bit 23 and clear bit 3 of register 0x84 */
+		printk(KERN_WARNING "BIOS didn't enabled PCI standards compliance.\n");
 	}
 }
quirks.c renamed from quirks_original.c +9 -8
@@ -464,23 +464,24 @@
  * Following the PCI ordering rules is optional on the AMD762. I'm not
  * sure what the designers were smoking but let's not inhale...
  *
- * To be fair to AMD, it follows the spec by default, its BIOS people
- * who turn it off!
+ * In fact, AMD even recommends to don't follow PCI standards
+ * in the section "Recommended BIOS settings" of the datasheet
  */
  
 static void __init quirk_amd_ordering(struct pci_dev *dev)
 {
 	u32 pcic;
+
+	printk(KERN_WARNING "Setting AMD recommended values for PCI bus. It isn't fully PCI standards compliant\n");
+
 	pci_read_config_dword(dev, 0x4C, &pcic);
-	if((pcic&6)!=6)
-	{
-		pcic |= 6;
-		printk(KERN_WARNING "BIOS failed to enable PCI standards compliance, fixing this error.\n");
+	pcic &= ~((u32)6);
 		pci_write_config_dword(dev, 0x4C, pcic);
+
 		pci_read_config_dword(dev, 0x84, &pcic);
-		pcic |= (1<<23);	/* Required in this mode */
+	pcic &= ~((u32)(1<<23));
+	pcic |= (1<<3);
 		pci_write_config_dword(dev, 0x84, pcic);
-	}
 }
 
 #ifdef CONFIG_X86_IO_APIC
author
#5 lore raw
Quoted 2 lines · xi

* patch_AMD762_PCI_compliance_set_by_bios.diff : lets the BIOS decide about PCI configuration

Breaks i2o with a 1004 BIOS on the ASUS dual athlon setup

Quoted 3 lines

* patch_AMD762_PCI_default_AMD_settings.diff : follow AMD recommendations but not PCI specs.

Looks better