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

sundeep subbaraya
2019-11-18T07:31:54Z

Hi Bjorn,

On Tue, Nov 12, 2019 at 5:08 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> 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.
>

Looks good. Thanks for applying the patch.

Sundeep

> > ---
> > 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;
> }
>