Re: [PATCH 01/14] PCI/P2PDMA: Add constants for not-supported result upstream_bridge_distance()

Koenig, Christian
2019-07-23T16:20:50Z

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)