| Message ID | 20210610160609.28447-2-logang@deltatee.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Bjorn Helgaas |
| Headers | show |
| Series | P2PDMA Cleanup | expand |
On Thu, Jun 10, 2021 at 10:06:04AM -0600, Logan Gunthorpe wrote: > The function upstream_bridge_distance() has evolved such that it's name > is no longer entirely reflective of what the function does. > > The function not only calculates the distance between two peers but also > calculates how the DMA addresses for those two peers should be mapped. > > Thus, rename the function to calc_map_type_and_dist() and rework the > documentation to better describe the two pieces of information the > function returns. > > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > --- > drivers/pci/p2pdma.c | 63 ++++++++++++++++++++++---------------------- > 1 file changed, 32 insertions(+), 31 deletions(-) > > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index 196382630363..6f90e9812f6e 100644 > --- a/drivers/pci/p2pdma.c > +++ b/drivers/pci/p2pdma.c > @@ -354,7 +354,7 @@ static bool host_bridge_whitelist(struct pci_dev *a, struct pci_dev *b) > } > > static enum pci_p2pdma_map_type > -__upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client, > +__calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client, > int *dist, bool *acs_redirects, struct seq_buf *acs_list) > { > struct pci_dev *a = provider, *b = client, *bb; > @@ -433,17 +433,18 @@ static unsigned long map_types_idx(struct pci_dev *client) > } > > /* > - * Find the distance through the nearest common upstream bridge between > - * two PCI devices. > + * Calculate the P2PDMA mapping type and distance between two PCI devices. > * > - * If the two devices are the same device then 0 will be returned. > + * If the two devices are the same device then PCI_P2PDMA_MAP_BUS_ADDR > + * and a distance of 0 will be returned. > * > * If there are two virtual functions of the same device behind the same > - * bridge port then 2 will be returned (one step down to the PCIe switch, > - * then one step back to the same device). > + * bridge port then PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 will be > + * returned (one step down to the PCIe switch, then one step back to the > + * same device). The new text is: If there are two virtual functions of the same device behind the same bridge port then PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 will be returned (one step down to the PCIe switch, then one step back to the same device). I *think* this includes two functions of the same multi-function device, or two virtual functions of the same device, right? In both cases, the two devices are obviously behind the same bridge port. Is this usage of "down to the PCIe switch" the common usage in P2PDMA? I normally think of going from an endpoint to a switch as being "up" toward the CPU. But PCIe made it all confusing by putting downstream ports at the upstream end of links and vice versa. We also have a bit of a mix in terminology between "bridge," "switch," "bridge port." I'd probably write something like: If they are two functions of the same device behind the same bridge, return PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 (one hop up to the bridge, then one hop back down to another function of the same device). No need to repost for this; just let me know what you think and I can tweak accordingly. Bjorn
On 2021-06-10 4:05 p.m., Bjorn Helgaas wrote: > The new text is: > > If there are two virtual functions of the same device behind the same > bridge port then PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 will be > returned (one step down to the PCIe switch, then one step back to the > same device). > > I *think* this includes two functions of the same multi-function > device, or two virtual functions of the same device, right? In both > cases, the two devices are obviously behind the same bridge port. Yes, that's correct, if it's the same device it must be behind the same bridge port; so dropping the "behind the same bridge port" is a good idea. > > Is this usage of "down to the PCIe switch" the common usage in P2PDMA? > I normally think of going from an endpoint to a switch as being "up" > toward the CPU. But PCIe made it all confusing by putting downstream > ports at the upstream end of links and vice versa. Good point. I've been casually saying "down to", but you are right "up" makes a lot more sense given the downstream/upstream terminology. > We also have a bit of a mix in terminology between "bridge," "switch," > "bridge port." I'd probably write something like: > > If they are two functions of the same device behind the same bridge, > return PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 (one hop up to > the bridge, then one hop back down to another function of the same > device). > > No need to repost for this; just let me know what you think and I can > tweak accordingly. What you've written sounds good to me, but I might have just dropped the "behind the same bridge" entirely given your feedback above. Thanks! Logan
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c index 196382630363..6f90e9812f6e 100644 --- a/drivers/pci/p2pdma.c +++ b/drivers/pci/p2pdma.c @@ -354,7 +354,7 @@ static bool host_bridge_whitelist(struct pci_dev *a, struct pci_dev *b) } static enum pci_p2pdma_map_type -__upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client, +__calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client, int *dist, bool *acs_redirects, struct seq_buf *acs_list) { struct pci_dev *a = provider, *b = client, *bb; @@ -433,17 +433,18 @@ static unsigned long map_types_idx(struct pci_dev *client) } /* - * Find the distance through the nearest common upstream bridge between - * two PCI devices. + * Calculate the P2PDMA mapping type and distance between two PCI devices. * - * If the two devices are the same device then 0 will be returned. + * If the two devices are the same device then PCI_P2PDMA_MAP_BUS_ADDR + * and a distance of 0 will be returned. * * If there are two virtual functions of the same device behind the same - * bridge port then 2 will be returned (one step down to the PCIe switch, - * then one step back to the same device). + * bridge port then PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 will be + * returned (one step down to the PCIe switch, then one step back to the + * same device). * * In the case where two devices are connected to the same PCIe switch, the - * value 4 will be returned. This corresponds to the following PCI tree: + * distance of 4 will be returned. This corresponds to the following PCI tree: * * -+ Root Port * \+ Switch Upstream Port @@ -454,31 +455,31 @@ static unsigned long map_types_idx(struct pci_dev *client) * * The distance is 4 because we traverse from Device A through the downstream * 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 cannot communicate using p2pdma will return - * PCI_P2PDMA_MAP_NOT_SUPPORTED. + * downstream port and then to Device B. The mapping type returned will depend + * on the ACS redirection setting of the bridges along the path. If ACS + * redirect is set on any bridge port in the path then the TLPs will go through + * the host bridge. Otherwise PCI_P2PDMA_MAP_BUS_ADDR is returned. * * 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, - * this function will return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE. - * - * If either bridge is not on the whitelist this function returns - * PCI_P2PDMA_MAP_NOT_SUPPORTED. + * will consult a whitelist. If the host bridge is in the whitelist, + * this function will return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE with the + * distance set to the number of ports per above. If the device is not + * in the whitelist the type will be returned PCI_P2PDMA_MAP_NOT_SUPPORTED. * - * If a bridge which has any ACS redirection bits set is in the path, - * acs_redirects will be set to true. In this case, a list of all infringing - * bridge addresses will be populated in acs_list (assuming it's non-null) - * for printk purposes. + * If any ACS redirect bits are set, then the acs_redirects boolean will be + * set to true and their pci device name will be appended to the acs_list + * seq_buf. This seq_buf is used to print a warning informing the user + * how to disable ACS using a command line parameter. + * (See calc_map_type_and_dist_warn() below) */ static enum pci_p2pdma_map_type -upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client, +calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client, int *dist, bool *acs_redirects, struct seq_buf *acs_list) { enum pci_p2pdma_map_type map_type; - map_type = __upstream_bridge_distance(provider, client, dist, - acs_redirects, acs_list); + map_type = __calc_map_type_and_dist(provider, client, dist, + acs_redirects, acs_list); if (map_type == PCI_P2PDMA_MAP_THRU_HOST_BRIDGE) { if (!cpu_supports_p2pdma() && @@ -494,8 +495,8 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client, } static enum pci_p2pdma_map_type -upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client, - int *dist) +calc_map_type_and_dist_warn(struct pci_dev *provider, struct pci_dev *client, + int *dist) { struct seq_buf acs_list; bool acs_redirects; @@ -505,8 +506,8 @@ upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client, if (!acs_list.buffer) return -ENOMEM; - ret = upstream_bridge_distance(provider, client, dist, &acs_redirects, - &acs_list); + ret = calc_map_type_and_dist(provider, client, dist, &acs_redirects, + &acs_list); if (acs_redirects) { pci_warn(client, "ACS redirect is set between the client and provider (%s)\n", pci_name(provider)); @@ -565,11 +566,11 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients, } if (verbose) - ret = upstream_bridge_distance_warn(provider, - pci_client, &distance); + ret = calc_map_type_and_dist_warn(provider, pci_client, + &distance); else - ret = upstream_bridge_distance(provider, pci_client, - &distance, NULL, NULL); + ret = calc_map_type_and_dist(provider, pci_client, + &distance, NULL, NULL); pci_dev_put(pci_client);
The function upstream_bridge_distance() has evolved such that it's name is no longer entirely reflective of what the function does. The function not only calculates the distance between two peers but also calculates how the DMA addresses for those two peers should be mapped. Thus, rename the function to calc_map_type_and_dist() and rework the documentation to better describe the two pieces of information the function returns. Signed-off-by: Logan Gunthorpe <logang@deltatee.com> --- drivers/pci/p2pdma.c | 63 ++++++++++++++++++++++---------------------- 1 file changed, 32 insertions(+), 31 deletions(-)