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Message-ID: <20181128215545.GC178809@google.com>
Date: Wed, 28 Nov 2018 15:55:45 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: sundeep.lkml@...il.com
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
sean.stalley@...el.com, sgoutham@...vell.com,
Subbaraya Sundeep <sbhatta@...vell.com>
Subject: Re: [PATCH v2] PCI: assign bus numbers present in EA capability for
bridges
On Mon, Nov 19, 2018 at 06:44:32PM +0530, sundeep.lkml@...il.com wrote:
> From: Subbaraya Sundeep <sbhatta@...vell.com>
>
> As per the spec, bridges with EA capability work
> with fixed secondary and subordinate bus numbers.
> Hence assign bus numbers to bridges from EA if the
> capability exists.
A reference to the spec section would be good, i.e., PCIe r4.0, sec xxx.
> Signed-off-by: Subbaraya Sundeep <sbhatta@...vell.com>
> ---
> Changes for v2:
> No changes just added Sean Stalley who did EA support for BARs.
>
> drivers/pci/probe.c | 58 ++++++++++++++++++++++++++++++++++++++++---
> include/uapi/linux/pci_regs.h | 6 +++++
> 2 files changed, 60 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index b1c05b5..f41d2e6 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1030,6 +1030,40 @@ static void pci_enable_crs(struct pci_dev *pdev)
>
> static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
> unsigned int available_buses);
> +/*
> + * pci_ea_fixed_busnrs() - Read fixed Secondary and Subordinate bus
> + * numbers from EA capability.
> + * @dev: Bridge with EA
> + * @secondary: updated with secondary bus number in EA
> + * @subordinate: updated with subordinate bus number in EA
> + *
> + * If it is a bridge with EA capability then fixed bus numbers are
> + * read from EA capability list and secondary, subordinate reference
> + * variables will be updated. Otherwise secondary and subordinate reference
> + * variables will be zeroed.
> + */
> +static void pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *secondary,
> + u8 *subordinate)
> +{
> + int ea;
> + int offset;
> + u32 dw;
> +
> + *secondary = *subordinate = 0;
> +
> + if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
> + return;
> +
> + /* find PCI EA capability in list */
> + ea = pci_find_capability(dev, PCI_CAP_ID_EA);
> + if (!ea)
> + return;
> +
> + offset = ea + PCI_EA_FIRST_ENT;
> + pci_read_config_dword(dev, offset, &dw);
"Num Entries" in the first DW of the capability is allowed to be zero,
in which case this word (the second DW) is invalid. [See comments
below; this code would be valid based on the 2014 ECN, but not per the
2017 PCIe r4.0 spec]
It would be much better if this function could be somehow incorporated
into pci_ea_init(), which already knows how to parse much of the EA
capability.
> + *secondary = dw & PCI_EA_SEC_BUS_MASK;
> + *subordinate = (dw & PCI_EA_SUB_BUS_MASK) >> PCI_EA_SUB_BUS_SHIFT;
> +}
>
> /*
> * pci_scan_bridge_extend() - Scan buses behind a bridge
> @@ -1064,6 +1098,8 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> u16 bctl;
> u8 primary, secondary, subordinate;
> int broken = 0;
> + u8 fixed_sec, fixed_sub;
> + int next_busnr;
>
> /*
> * Make sure the bridge is powered on to be able to access config
> @@ -1163,17 +1199,25 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> /* Clear errors */
> pci_write_config_word(dev, PCI_STATUS, 0xffff);
>
> + /* read bus numbers from EA */
> + 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;
> +
> /*
> * Prevent assigning a bus number that already exists.
> * This can happen when a bridge is hot-plugged, so in this
> * case we only re-scan this bus.
> */
> - child = pci_find_bus(pci_domain_nr(bus), max+1);
> + child = pci_find_bus(pci_domain_nr(bus), next_busnr);
> if (!child) {
> - child = pci_add_new_bus(bus, dev, max+1);
> + child = pci_add_new_bus(bus, dev, next_busnr);
> if (!child)
> goto out;
> - pci_bus_insert_busn_res(child, max+1,
> + pci_bus_insert_busn_res(child, next_busnr,
> bus->busn_res.end);
> }
> max++;
> @@ -1234,7 +1278,13 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> max += i;
> }
>
> - /* Set subordinate bus number to its real value */
> + /*
> + * Set subordinate bus number to its real value.
> + * If fixed subordinate bus number exists from EA
> + * capability then use it.
> + */
> + if (fixed_sub)
> + max = fixed_sub;
> pci_bus_update_busn_res_end(child, max);
> pci_write_config_byte(dev, PCI_SUBORDINATE_BUS, max);
> }
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index e1e9888..c3d0904 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -372,6 +372,12 @@
> #define PCI_EA_FIRST_ENT_BRIDGE 8 /* First EA Entry for Bridges */
You didn't add PCI_EA_FIRST_ENT_BRIDGE (Sean did with f80b0ba95964
("PCI: Add Enhanced Allocation register entries")), but it is unused
and I can't match it with anything in the spec (PCIe r4.0, sec 7.8.5).
It might be related to the code in pci_ea_init() that skips DWORD 2
for type 1 functions. But I still don't see that in the spec.
If it's obsolete, we should remove it (with a separate patch).
Hmm, I do see this in the ECN dated 23 Oct 2014, sec 6.9.1.2. But
presumably that would be incorporated in PCIe r4.0, which is dated 27
Sep 2017.
I have no idea what to do with this. I can't merge this without some
clarification here,
> #define PCI_EA_ES 0x00000007 /* Entry Size */
> #define PCI_EA_BEI 0x000000f0 /* BAR Equivalent Indicator */
> +
> +/* EA fixed Secondary and Subordinate bus numbers for Bridge */
> +#define PCI_EA_SEC_BUS_MASK 0xff
> +#define PCI_EA_SUB_BUS_MASK 0xff00
> +#define PCI_EA_SUB_BUS_SHIFT 8
> +
> /* 0-5 map to BARs 0-5 respectively */
> #define PCI_EA_BEI_BAR0 0
> #define PCI_EA_BEI_BAR5 5
> --
> 1.8.3.1
>
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