1 PCI with Driver Model 2 ===================== 3 4 How busses are scanned 5 ---------------------- 6 7 Any config read will end up at pci_read_config(). This uses 8 uclass_get_device_by_seq() to get the PCI bus for a particular bus number. 9 Bus number 0 will need to be requested first, and the alias in the device 10 tree file will point to the correct device: 11 12 13 aliases { 14 pci0 = &pci; 15 }; 16 17 pci: pci-controller { 18 compatible = "sandbox,pci"; 19 ... 20 }; 21 22 23 If there is no alias the devices will be numbered sequentially in the device 24 tree. 25 26 The call to uclass_get_device() will cause the PCI bus to be probed. 27 This does a scan of the bus to locate available devices. These devices are 28 bound to their appropriate driver if available. If there is no driver, then 29 they are bound to a generic PCI driver which does nothing. 30 31 After probing a bus, the available devices will appear in the device tree 32 under that bus. 33 34 Note that this is all done on a lazy basis, as needed, so until something is 35 touched on PCI (eg: a call to pci_find_devices()) it will not be probed. 36 37 PCI devices can appear in the flattened device tree. If they do this serves to 38 specify the driver to use for the device. In this case they will be bound at 39 first. Each PCI device node must have a compatible string list as well as a 40 <reg> property, as defined by the IEEE Std 1275-1994 PCI bus binding document 41 v2.1. Note we must describe PCI devices with the same bus hierarchy as the 42 hardware, otherwise driver model cannot detect the correct parent/children 43 relationship during PCI bus enumeration thus PCI devices won't be bound to 44 their drivers accordingly. A working example like below: 45 46 pci { 47 #address-cells = <3>; 48 #size-cells = <2>; 49 compatible = "pci-x86"; 50 u-boot,dm-pre-reloc; 51 ranges = <0x02000000 0x0 0x40000000 0x40000000 0 0x80000000 52 0x42000000 0x0 0xc0000000 0xc0000000 0 0x20000000 53 0x01000000 0x0 0x2000 0x2000 0 0xe000>; 54 55 pcie@17,0 { 56 #address-cells = <3>; 57 #size-cells = <2>; 58 compatible = "pci-bridge"; 59 u-boot,dm-pre-reloc; 60 reg = <0x0000b800 0x0 0x0 0x0 0x0>; 61 62 topcliff@0,0 { 63 #address-cells = <3>; 64 #size-cells = <2>; 65 compatible = "pci-bridge"; 66 u-boot,dm-pre-reloc; 67 reg = <0x00010000 0x0 0x0 0x0 0x0>; 68 69 pciuart0: uart@a,1 { 70 compatible = "pci8086,8811.00", 71 "pci8086,8811", 72 "pciclass,070002", 73 "pciclass,0700", 74 "x86-uart"; 75 u-boot,dm-pre-reloc; 76 reg = <0x00025100 0x0 0x0 0x0 0x0 77 0x01025110 0x0 0x0 0x0 0x0>; 78 ...... 79 }; 80 81 ...... 82 }; 83 }; 84 85 ...... 86 }; 87 88 In this example, the root PCI bus node is the "/pci" which matches "pci-x86" 89 driver. It has a subnode "pcie@17,0" with driver "pci-bridge". "pcie@17,0" 90 also has subnode "topcliff@0,0" which is a "pci-bridge" too. Under that bridge, 91 a PCI UART device "uart@a,1" is described. This exactly reflects the hardware 92 bus hierarchy: on the root PCI bus, there is a PCIe root port which connects 93 to a downstream device Topcliff chipset. Inside Topcliff chipset, it has a 94 PCIe-to-PCI bridge and all the chipset integrated devices like the PCI UART 95 device are on the PCI bus. Like other devices in the device tree, if we want 96 to bind PCI devices before relocation, "u-boot,dm-pre-reloc" must be declared 97 in each of these nodes. 98 99 If PCI devices are not listed in the device tree, U_BOOT_PCI_DEVICE can be used 100 to specify the driver to use for the device. The device tree takes precedence 101 over U_BOOT_PCI_DEVICE. Plese note with U_BOOT_PCI_DEVICE, only drivers with 102 DM_FLAG_PRE_RELOC will be bound before relocation. If neither device tree nor 103 U_BOOT_PCI_DEVICE is provided, the built-in driver (either pci_bridge_drv or 104 pci_generic_drv) will be used. 105 106 107 Sandbox 108 ------- 109 110 With sandbox we need a device emulator for each device on the bus since there 111 is no real PCI bus. This works by looking in the device tree node for a 112 driver. For example: 113 114 115 pci@1f,0 { 116 compatible = "pci-generic"; 117 reg = <0xf800 0 0 0 0>; 118 emul@1f,0 { 119 compatible = "sandbox,swap-case"; 120 }; 121 }; 122 123 This means that there is a 'sandbox,swap-case' driver at that bus position. 124 Note that the first cell in the 'reg' value is the bus/device/function. See 125 PCI_BDF() for the encoding (it is also specified in the IEEE Std 1275-1994 126 PCI bus binding document, v2.1) 127 128 When this bus is scanned we will end up with something like this: 129 130 `- * pci-controller @ 05c660c8, 0 131 `- pci@1f,0 @ 05c661c8, 63488 132 `- emul@1f,0 @ 05c662c8 133 134 When accesses go to the pci@1f,0 device they are forwarded to its child, the 135 emulator. 136
