[+cc linux-pci] On Wed, Aug 20, 2014 at 4:05 PM, Matevz Langus <matevz.langus@xxxxxxxx> wrote: > Hi, > > I would like to ask if somebody is aware of a correct way to change they way kernel aligns PCI resources. By default it uses minimal alignment of 1 MB. Do you mean alignment of bridge windows? Normal device BARs are aligned on their size, but mem bridge windows are aligned to a minimum of 1MB. This is a consequence of the fact that the low 20 bits of the bridge's Memory Base register are assumed to be zero (see PCI Bridge spec, r1.2, sec 3.2.5.8). Similarly, the low 20 bits of the Memory Limit register are assumed to be 0xfffff, which means the memory window is a multiple of 1MB in size. > Due to the hardware limitation I would need to change that down to 64 kB. With this change PCI Endpoints with many small BARs would fit into limited memory space available on the RC. > This could be useful for all smaller embedded systems. What's your system topology, e.g., can you share the complete "lspci -vv" output? If the bridge window alignment is an issue, it sounds like maybe you have several bridges. Each memory window will take at least 1MB of space. If you have, e.g., four bridges, with devices behind all of them, each bridge will require at least 1MB of memory space. If your RC only has 2MB of MMIO space, the bridges won't all fit. I/O port windows are normally a minimum of 64K, but we do support a quirk (see io_window_1k) that allows smaller windows on bridges that support it. If you have bridges with an extension to allow smaller memory windows, maybe we could do something similar. > It looks just changing aligns in pbus_size_mem (in file setup-bus.c) works but not with all PCI EP drivers. Some will crash during init. > > Regards, > Matevz Langus-- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- 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
