On Mon, Sep 02, 2019 at 09:00:03PM +0530, sundeep.lkml@xxxxxxxxx wrote:
> From: Subbaraya Sundeep <sbhatta@xxxxxxxxxxx>
>
> 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 can be zero
s/can/must/
The spec uses the term *must*. "Can" implies that this is optional.
> when no function that uses EA is located behind it.
> Hence assign bus numbers sequentially when fixed bus
> numbers are zero.
Perhaps s/sequentially/as per normal/ or similar. As we're not doing
anything different here.
>
> Fixes: 2dbce590117981196fe355efc0569bc6f949ae9b
Is it worth describing what actually goes wrong without this patch - and
when this occurs? I guess it's possible for a bridge to have an EA
capability, but no devices using EA behind it - and thus in this suitation
the downstream devices have unnecessary bus number constraints?
>
> Signed-off-by: Subbaraya Sundeep <sbhatta@xxxxxxxxxxx>
Does this need to be CC'd to stable?
> ---
> 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 a3c7338..c06ca4c 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1095,27 +1095,28 @@ 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;
Is there any value in doing any sanity checking here? E.g. sub !=0, sub > sec?
> - return true;
> }
>
> /*
> @@ -1151,7 +1152,6 @@ 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;
>
> @@ -1254,11 +1254,12 @@ 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;
There is a subtle style change here (assigning and then potentially reassigning
with a new value vs assigning once using both if/else). No idea if this matters
but I thought I'd point it out in case it wasn't intentional.
Thanks,
Andrew Murray
>
> /*
> * Prevent assigning a bus number that already exists.
> @@ -1336,7 +1337,7 @@ 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
>
