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    Subject[PATCH 01/14] PCI/P2PDMA: Add constants for not-supported result upstream_bridge_distance()
    Add constant flags to indicate two devices are not supported or whether
    the data path goes through the host bridge instead of using the negative
    values -1 and -2.

    This helps annotate the code better, but the main reason is so we
    can cache the result in an xarray which does not allow us to store
    negative values.

    Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
    ---
    drivers/pci/p2pdma.c | 52 ++++++++++++++++++++++++++------------------
    1 file changed, 31 insertions(+), 21 deletions(-)

    diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
    index 234476226529..e8ec86e1dd00 100644
    --- a/drivers/pci/p2pdma.c
    +++ b/drivers/pci/p2pdma.c
    @@ -273,6 +273,20 @@ static bool root_complex_whitelist(struct pci_dev *dev)
    return false;
    }

    +enum {
    + /*
    + * Thes arbitrary offset are or'd onto the upstream distance
    + * calculation for the following conditions:
    + */
    +
    + /* The data path includes the host-bridge */
    + P2PDMA_THRU_HOST_BRIDGE = 0x02000000,
    + /* The data path is forced through the host-bridge due to ACS */
    + P2PDMA_ACS_FORCES_UPSTREAM = 0x04000000,
    + /* The data path is not supported by P2PDMA */
    + P2PDMA_NOT_SUPPORTED = 0x08000000,
    +};
    +
    /*
    * Find the distance through the nearest common upstream bridge between
    * two PCI devices.
    @@ -297,22 +311,17 @@ static bool root_complex_whitelist(struct pci_dev *dev)
    * port of the switch, to the common upstream port, back up to the second
    * downstream port and then to Device B.
    *
    - * Any two devices that don't have a common upstream bridge will return -1.
    - * In this way devices on separate PCIe root ports will be rejected, which
    - * is what we want for peer-to-peer seeing each PCIe root port defines a
    - * separate hierarchy domain and there's no way to determine whether the root
    - * complex supports forwarding between them.
    + * Any two devices that cannot communicate using p2pdma will return the distance
    + * with the flag P2PDMA_NOT_SUPPORTED.
    *
    - * In the case where two devices are connected to different PCIe switches,
    - * this function will still return a positive distance as long as both
    - * switches eventually have a common upstream bridge. Note this covers
    - * the case of using multiple PCIe switches to achieve a desired level of
    - * fan-out from a root port. The exact distance will be a function of the
    - * number of switches between Device A and Device B.
    + * Any two devices that have a data path that goes through the host bridge
    + * will consult a whitelist. If the host bridges are on the whitelist,
    + * then the distance will be returned with the flag P2PDMA_THRU_HOST_BRIDGE set.
    + * If either bridge is not on the whitelist, the flag P2PDMA_NOT_SUPPORTED will
    + * be set.
    *
    * If a bridge which has any ACS redirection bits set is in the path
    - * then this functions will return -2. This is so we reject any
    - * cases where the TLPs are forwarded up into the root complex.
    + * then this functions will flag the result with P2PDMA_ACS_FORCES_UPSTREAM.
    * In this case, a list of all infringing bridge addresses will be
    * populated in acs_list (assuming it's non-null) for printk purposes.
    */
    @@ -359,9 +368,9 @@ static int upstream_bridge_distance(struct pci_dev *provider,
    */
    if (root_complex_whitelist(provider) &&
    root_complex_whitelist(client))
    - return 0x1000 + dist_a + dist_b;
    + return (dist_a + dist_b) | P2PDMA_THRU_HOST_BRIDGE;

    - return -1;
    + return (dist_a + dist_b) | P2PDMA_NOT_SUPPORTED;

    check_b_path_acs:
    bb = b;
    @@ -379,7 +388,7 @@ static int upstream_bridge_distance(struct pci_dev *provider,
    }

    if (acs_cnt)
    - return -2;
    + return P2PDMA_NOT_SUPPORTED | P2PDMA_ACS_FORCES_UPSTREAM;

    return dist_a + dist_b;
    }
    @@ -395,16 +404,17 @@ static int upstream_bridge_distance_warn(struct pci_dev *provider,
    return -ENOMEM;

    ret = upstream_bridge_distance(provider, client, &acs_list);
    - if (ret == -2) {
    - pci_warn(client, "cannot be used for peer-to-peer DMA as ACS redirect is set between the client and provider (%s)\n",
    + if (ret & P2PDMA_ACS_FORCES_UPSTREAM) {
    + pci_warn(client, "ACS redirect is set between the client and provider (%s)\n",
    pci_name(provider));
    /* Drop final semicolon */
    acs_list.buffer[acs_list.len-1] = 0;
    pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
    acs_list.buffer);
    + }

    - } else if (ret < 0) {
    - pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge\n",
    + if (ret & P2PDMA_NOT_SUPPORTED) {
    + pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge or whitelisted host bridge\n",
    pci_name(provider));
    }

    @@ -468,7 +478,7 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,

    pci_dev_put(pci_client);

    - if (ret < 0)
    + if (ret & P2PDMA_NOT_SUPPORTED)
    not_supported = true;

    if (not_supported && !verbose)
    --
    2.20.1
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