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    SubjectRe: [PATCH 01/14] PCI/P2PDMA: Add constants for not-supported result upstream_bridge_distance()
    Date
    Am 23.07.19 um 01:08 schrieb Logan Gunthorpe:
    > 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>

    Reviewed-by: Christian König <christian.koenig@amd.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)

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