Re: sparc64 PCI BAR allocation is still problematic

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Apr 10, 2018 at 09:45:09PM +0300, Meelis Roos wrote:
> > commit bc270e0028cd0856d5689cab38f0071f0d07b3be
> > Author: Bjorn Helgaas <bhelgaas@google.com>
> > Date:   Tue Apr 10 08:47:34 2018 -0500
> > 
> >     sparc/PCI: Request legacy VGA framebuffer only for VGA devices
> 
> Thank you.
> 
> It does not seem to compile for me:
> 
>   CC      arch/sparc/kernel/pci.o
> arch/sparc/kernel/pci.c: In function ‘pci_claim_legacy_resources’:
> arch/sparc/kernel/pci.c:644:26: error: ‘bus’ undeclared (first use in this function)
>   pcibios_bus_to_resource(bus, p, &region);

Oops, sorry, I can't easily compile test it.  Here's an updated patch:

commit a9ded309cbf3f57e9979848fd0aa0ffacdf11f1a
Author: Bjorn Helgaas <bhelgaas@google.com>
Date:   Tue Apr 10 08:47:34 2018 -0500

    sparc/PCI: Request legacy VGA framebuffer only for VGA devices
    
    Previously we unconditionally requested the legacy VGA framebuffer (bus
    address 0xa0000-0xbffff) before we even know what PCI devices are present,
    in these paths:
    
      pci_fire_pbm_init, schizo_pbm_init, pci_sun4v_pbm_init, psycho_pbm_init_common
        pci_determine_mem_io_space
          pci_register_legacy_regions
            p->start = mem_res->start + 0xa0000
            request_resource(mem_res, p)    # claim VGA framebuffer
        pci_scan_one_pbm
          pci_of_scan_bus                   # scan DT for PCI devices
          pci_claim_bus_resources           # claim PCI device BARs
    
    If we found a PCI device with a BAR that overlapped the framebuffer area,
    we complained about not being able to claim the BAR, e.g.,
    
      pci_bus 0002:00: root bus resource [mem 0x7ff00000000-0x7ffffffffff] (bus address [0x00000000-0xffffffff])
      pci 0002:00:07.0: can't claim BAR 1 [mem 0x7ff00000000-0x7ff000fffff]: address conflict with Video RAM area [??? 0x7ff000a0000-0x7ff000bffff flags 0x80000000]
    
    If there is no VGA device in the same PCI segment, there's no reason to
    reserve the framebuffer and there's no conflict.
    
    If there *is* a VGA device in the same segment, both the VGA device and the
    device with an overlapping BAR may respond to the framebuffer addresses,
    which may cause bus errors.
    
    Request the legacy framebuffer area only when we actually find a VGA
    device.  This is not sparc-specific and could be made more generic in the
    PCI core eventually.
    
    Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=117191
    Reported-by: Meelis Roos <mroos@linux.ee>

diff --git a/arch/sparc/kernel/pci.c b/arch/sparc/kernel/pci.c
index 41b20edb427d..d5360e941620 100644
--- a/arch/sparc/kernel/pci.c
+++ b/arch/sparc/kernel/pci.c
@@ -624,6 +624,44 @@ static void pci_bus_register_of_sysfs(struct pci_bus *bus)
 		pci_bus_register_of_sysfs(child_bus);
 }
 
+static void pci_claim_legacy_resources(struct pci_dev *dev)
+{
+	struct pci_bus_region region;
+	struct resource *p, *root, *conflict;
+
+	if ((dev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
+		return;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return;
+
+	p->name = "Video RAM area";
+	p->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
+
+	region.start = 0xa0000UL;
+	region.end = region.start + 0x1ffffUL;
+	pcibios_bus_to_resource(dev->bus, p, &region);
+
+	root = pci_find_parent_resource(dev, p);
+	if (!root) {
+		pci_info(dev, "can't claim VGA legacy %pR: no compatible bridge window\n", p);
+		goto err;
+	}
+
+	conflict = request_resource_conflict(root, p);
+	if (conflict) {
+		pci_info(dev, "can't claim VGA legacy %pR: address conflict with %s %pR\n",
+			 p, conflict->name, conflict);
+		goto err;
+	}
+
+	return;
+
+err:
+	kfree(p);
+}
+
 static void pci_claim_bus_resources(struct pci_bus *bus)
 {
 	struct pci_bus *child_bus;
@@ -648,6 +686,8 @@ static void pci_claim_bus_resources(struct pci_bus *bus)
 
 			pci_claim_resource(dev, i);
 		}
+
+		pci_claim_legacy_resources(dev);
 	}
 
 	list_for_each_entry(child_bus, &bus->children, node)
@@ -687,6 +727,7 @@ struct pci_bus *pci_scan_one_pbm(struct pci_pbm_info *pbm,
 	pci_bus_register_of_sysfs(bus);
 
 	pci_claim_bus_resources(bus);
+
 	pci_bus_add_devices(bus);
 	return bus;
 }
diff --git a/arch/sparc/kernel/pci_common.c b/arch/sparc/kernel/pci_common.c
index 38d46bcc8634..9bb6a192ef3f 100644
--- a/arch/sparc/kernel/pci_common.c
+++ b/arch/sparc/kernel/pci_common.c
@@ -329,23 +329,6 @@ void pci_get_pbm_props(struct pci_pbm_info *pbm)
 	}
 }
 
-static void pci_register_legacy_regions(struct resource *io_res,
-					struct resource *mem_res)
-{
-	struct resource *p;
-
-	/* VGA Video RAM. */
-	p = kzalloc(sizeof(*p), GFP_KERNEL);
-	if (!p)
-		return;
-
-	p->name = "Video RAM area";
-	p->start = mem_res->start + 0xa0000UL;
-	p->end = p->start + 0x1ffffUL;
-	p->flags = IORESOURCE_BUSY;
-	request_resource(mem_res, p);
-}
-
 static void pci_register_iommu_region(struct pci_pbm_info *pbm)
 {
 	const u32 *vdma = of_get_property(pbm->op->dev.of_node, "virtual-dma",
@@ -487,8 +470,6 @@ void pci_determine_mem_io_space(struct pci_pbm_info *pbm)
 	if (pbm->mem64_space.flags)
 		request_resource(&iomem_resource, &pbm->mem64_space);
 
-	pci_register_legacy_regions(&pbm->io_space,
-				    &pbm->mem_space);
 	pci_register_iommu_region(pbm);
 }