On Tue, Jul 17, 2012 at 07:16:59PM +1000, Benjamin Herrenschmidt wrote: > On Tue, 2012-07-17 at 13:57 +0800, Ram Pai wrote: > > Hmm.. this code is not about determining what kind of segment the > > platform is returning. This code is about using the right alignment > > constraints for the type of segment from which resource will be > > allocated. right? > > > > b_res is the resource that is being sized. b_res already knows > > what kind of resource it is, i.e IORESOURCE_MEM or > > IORESOURCE_PREFETCH. > > Hence we should be exactly using the same alignment constraints as > > that dictated by the type of b_res. no? > > This is unclear.... ideally we want to know which of the host bridge > "apertures" is about to be used... > > IE. A prefetchable resource can very well be allocated to a > non-prefetchable window, though the other way isn't supposed to happen. > > Additionally, our PHB doesn't actually differenciate prefetchable and > non-prefetchable windows (whether you can prefetch or not is an > attribute of the CPU mapping, but basically non-cachable mappings are > never prefetchable for us). > > So we can be lax in how we assign things between our single 32-bit > window divided in 128 segments and our 16x64-bit windows divided in 8 > segments (and future HW will do thins differently even). > > For example we would like in some cases to use M64's (64-bit windows) to > map SR-IOV BARs regardless of the "prefetchability" though that can only > work if we are not behind a PCIe switch, as those are technically > allowed to prefetch :-) > > Worst is that the alignment constraint is based on the segment size, and > while we more/less fix the size of the 32-bit window, we plan to > dynamically allocate/resize the 64-bit ones which will mean variable > segment sizes as well. > > So the more information you can get at that point, the better. The type > is useful because it allows us to know if you are trying to put a > prefetchable memory BAR inside a non-prefetchable region, in which case > we know it has to be in M32. Ben, Lets say we passed that 'type' flag to size the minimum alignment constraints for that b_res. And window_alignment(bus, type) of your platform used that 'type' information to determine whether to use the alignment constraints of 32-bit window or 64-bit window. However, later when the b_res is actually allocated a resource, the pci_assign_resource() has no idea whether to allocate 32-bit window resource or 64-bit window resource, because the 'type' information is not captured anywhere in b_res. You would basically have a disconnect between what is sized and what is allocated. Unless offcourse you pass that 'type' to the b_res->flags, which is currently not the case. RP -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
