Re: [v2 PATCH] PCI: Do not use bus number zero from EA capability

Bjorn Helgaas
2019-11-11T23:38:04Z

On Mon, Nov 04, 2019 at 12:27:44PM +0530, sundeep.lkml@gmail.com wrote:
> From: Subbaraya Sundeep <sbhatta@marvell.com>
>
> As per the spec, "Enhanced Allocation (EA) for Memory
> and I/O Resources" ECN, approved 23 October 2014,
> sec 6.9.1.2, fixed bus numbers of a bridge must be zero
> when no function that uses EA is located behind it.
> Hence assign bus numbers normally instead of assigning
> zeroes from EA capability. Failing to do this and using
> zeroes from EA would make the bridges non-functional.
>
> Fixes: '2dbce5901179 ("PCI: Assign bus numbers present in
> EA capability for bridges")'
> Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
> Cc: stable@vger.kernel.org # v5.2+

Applied to pci/resource for v5.5, thanks!

I tweaked it as below so the logic about how to interpret the EA Fixed
Secondary Bus Number is more localized. Let me know if that doesn't
make sense.

> ---
> drivers/pci/probe.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 3d5271a..116b276 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1090,27 +1090,28 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
> * @sub: updated with subordinate bus number from EA
> *
> * If @dev is a bridge with EA capability, update @sec and @sub with
> - * fixed bus numbers from the capability and return true. Otherwise,
> - * return false.
> + * fixed bus numbers from the capability. Otherwise @sec and @sub
> + * will be zeroed.
> */
> -static bool pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)
> +static void pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)
> {
> int ea, offset;
> u32 dw;
>
> + *sec = *sub = 0;
> +
> if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
> - return false;
> + return;
>
> /* find PCI EA capability in list */
> ea = pci_find_capability(dev, PCI_CAP_ID_EA);
> if (!ea)
> - return false;
> + return;
>
> offset = ea + PCI_EA_FIRST_ENT;
> pci_read_config_dword(dev, offset, &dw);
> *sec = dw & PCI_EA_SEC_BUS_MASK;
> *sub = (dw & PCI_EA_SUB_BUS_MASK) >> PCI_EA_SUB_BUS_SHIFT;
> - return true;
> }
>
> /*
> @@ -1146,7 +1147,6 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> u16 bctl;
> u8 primary, secondary, subordinate;
> int broken = 0;
> - bool fixed_buses;
> u8 fixed_sec, fixed_sub;
> int next_busnr;
>
> @@ -1249,11 +1249,12 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> pci_write_config_word(dev, PCI_STATUS, 0xffff);
>
> /* Read bus numbers from EA Capability (if present) */
> - fixed_buses = pci_ea_fixed_busnrs(dev, &fixed_sec, &fixed_sub);
> - if (fixed_buses)
> + pci_ea_fixed_busnrs(dev, &fixed_sec, &fixed_sub);
> +
> + next_busnr = max + 1;
> + /* Use secondary bus number in EA */
> + if (fixed_sec)
> next_busnr = fixed_sec;
> - else
> - next_busnr = max + 1;
>
> /*
> * Prevent assigning a bus number that already exists.
> @@ -1331,7 +1332,7 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> * If fixed subordinate bus number exists from EA
> * capability then use it.
> */
> - if (fixed_buses)
> + if (fixed_sub)
> max = fixed_sub;
> pci_bus_update_busn_res_end(child, max);
> pci_write_config_byte(dev, PCI_SUBORDINATE_BUS, max);
> --
> 2.7.4
>

commit 25328e0447de ("PCI: Do not use bus number zero from EA capability")
Author: Subbaraya Sundeep <sbhatta@marvell.com>
Date: Mon Nov 4 12:27:44 2019 +0530

PCI: Do not use bus number zero from EA capability

As per PCIe r5.0, sec 7.8.5.2, fixed bus numbers of a bridge must be zero
when no function that uses EA is located behind it. Hence, if EA supplies
bus numbers of zero, assign bus numbers normally. A secondary bus can
never have a bus number of zero, so setting a bridge's Secondary Bus Number
to zero makes downstream devices unreachable.

[bhelgaas: retain bool return value so "zero is invalid" logic is local]
Fixes: 2dbce5901179 ("PCI: Assign bus numbers present in EA capability for bridges")
Link: https://lore.kernel.org/r/1572850664-9861-1-git-send-email-sundeep.lkml@gmail.com
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org # v5.2+

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index bdbc8490f962..d3033873395d 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1090,14 +1090,15 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
* @sec: updated with secondary bus number from EA
* @sub: updated with subordinate bus number from EA
*
- * If @dev is a bridge with EA capability, update @sec and @sub with
- * fixed bus numbers from the capability and return true. Otherwise,
- * return false.
+ * If @dev is a bridge with EA capability that specifies valid secondary
+ * and subordinate bus numbers, return true with the bus numbers in @sec
+ * and @sub. Otherwise return false.
*/
static bool pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)
{
int ea, offset;
u32 dw;
+ u8 ea_sec, ea_sub;

if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
return false;
@@ -1109,8 +1110,13 @@ static bool pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)

offset = ea + PCI_EA_FIRST_ENT;
pci_read_config_dword(dev, offset, &dw);
- *sec = dw & PCI_EA_SEC_BUS_MASK;
- *sub = (dw & PCI_EA_SUB_BUS_MASK) >> PCI_EA_SUB_BUS_SHIFT;
+ ea_sec = dw & PCI_EA_SEC_BUS_MASK;
+ ea_sub = (dw & PCI_EA_SUB_BUS_MASK) >> PCI_EA_SUB_BUS_SHIFT;
+ if (ea_sec == 0 || ea_sub < ea_sec)
+ return false;
+
+ *sec = ea_sec;
+ *sub = ea_sub;
return true;
}