On Tue, Feb 13, 2018 at 2:15 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > On Tue, Feb 13, 2018 at 12:24:40PM -0800, Andrey Smirnov wrote: >> On Tue, Feb 13, 2018 at 10:13 AM, Michael S. Tsirkin <m...@redhat.com> wrote: >> > On Tue, Feb 13, 2018 at 09:07:10AM -0800, Andrey Smirnov wrote: >> >> +static void designware_pcie_root_class_init(ObjectClass *klass, void >> >> *data) >> >> +{ >> >> + PCIDeviceClass *k = PCI_DEVICE_CLASS(klass); >> >> + DeviceClass *dc = DEVICE_CLASS(klass); >> >> + >> >> + set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories); >> >> + >> >> + k->vendor_id = PCI_VENDOR_ID_SYNOPSYS; >> >> + k->device_id = 0xABCD; >> >> + k->revision = 0; >> >> + k->class_id = PCI_CLASS_BRIDGE_PCI; >> >> + k->is_express = true; >> >> + k->is_bridge = true; >> >> + k->exit = pci_bridge_exitfn; >> >> + k->realize = designware_pcie_root_realize; >> >> + k->config_read = designware_pcie_root_config_read; >> >> + k->config_write = designware_pcie_root_config_write; >> >> + >> >> + dc->reset = pci_bridge_reset; >> >> + /* >> >> + * PCI-facing part of the host bridge, not usable without the >> >> + * host-facing part, which can't be device_add'ed, yet. >> >> + */ >> >> + dc->user_creatable = false; >> >> + dc->vmsd = &vmstate_designware_pcie_root; >> >> +} >> >> + >> >> +static uint64_t designware_pcie_host_mmio_read(void *opaque, hwaddr addr, >> >> + unsigned int size) >> >> +{ >> >> + PCIHostState *pci = PCI_HOST_BRIDGE(opaque); >> >> + PCIDevice *device = pci_find_device(pci->bus, 0, 0); >> >> + >> >> + return pci_host_config_read_common(device, >> >> + addr, >> >> + pci_config_size(device), >> >> + size); >> >> +} >> >> + >> >> +static void designware_pcie_host_mmio_write(void *opaque, hwaddr addr, >> >> + uint64_t val, unsigned int >> >> size) >> >> +{ >> >> + PCIHostState *pci = PCI_HOST_BRIDGE(opaque); >> >> + PCIDevice *device = pci_find_device(pci->bus, 0, 0); >> >> + >> >> + return pci_host_config_write_common(device, >> >> + addr, >> >> + pci_config_size(device), >> >> + val, size); >> >> +} >> >> + >> >> +static const MemoryRegionOps designware_pci_mmio_ops = { >> >> + .read = designware_pcie_host_mmio_read, >> >> + .write = designware_pcie_host_mmio_write, >> >> + .endianness = DEVICE_NATIVE_ENDIAN, >> >> + .impl = { >> >> + /* >> >> + * Our device would not work correctly if the guest was doing >> >> + * unaligned access. This might not be a limitation on the real >> >> + * device but in practice there is no reason for a guest to >> >> access >> >> + * this device unaligned. >> >> + */ >> >> + .min_access_size = 4, >> >> + .max_access_size = 4, >> >> + .unaligned = false, >> >> + }, >> >> +}; >> > >> > Could you pls add some comments explaining why is DEVICE_NATIVE_ENDIAN >> > appropriate here? Most of these cases are plain "we never bothered >> > about cross-endian setups". Some are "there's a mix of different >> > endian-ness values, need to handle in a special way". >> > >> > I suspect you really need DEVICE_LITTLE_ENDIAN. >> > >> >> That MemoryRegion corresponds to a register file permanently mapped >> into CPU's address space, so my assumption is that SoC designers will >> wire it according to CPUs endianness be it big or little. I am not >> aware of any big-endian CPU based SoC on the market using Designware's >> IP block, so I don't think there are any precedent confirming or >> denying correctness of my assumption. IMHO, this is also the reason >> why all of Linux driver code for that IP assumes little endianness. > > IMHO if Linux driver code does cpu_to_le then it seems best to be > consistent with that. >
Well, all of the DW code does so implicitly by using readl()/writel() helpers which will perform cpu_to_le/le_to_cpu under the hood. But is seems to me that it could be either because the access does have to be LE always or simply because readl()/writel() are goto memory helpers on ARM/LE-platforms. FWIW: Somewhat similar precedent of MIPS/Boston machine can serve as counter-example to my assumption, since Xilinx PCIE IP there seem to be wired to be LE despite being attached to BE CPU. Thanks, Andrey Smirnov