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947eb4396d
Correct two typos and mention how pci bus will be probed. Signed-off-by: Bin Meng <bmeng.cn@gmail.com> Acked-by: Simon Glass <sjg@chromium.org>
70 lines
2 KiB
Text
70 lines
2 KiB
Text
PCI with Driver Model
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=====================
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How busses are scanned
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----------------------
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Any config read will end up at pci_read_config(). This uses
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uclass_get_device_by_seq() to get the PCI bus for a particular bus number.
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Bus number 0 will need to be requested first, and the alias in the device
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tree file will point to the correct device:
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aliases {
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pci0 = &pci;
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};
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pci: pci-controller {
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compatible = "sandbox,pci";
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...
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};
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If there is no alias the devices will be numbered sequentially in the device
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tree.
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The call to uclass_get_device() will cause the PCI bus to be probed.
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This does a scan of the bus to locate available devices. These devices are
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bound to their appropriate driver if available. If there is no driver, then
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they are bound to a generic PCI driver which does nothing.
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After probing a bus, the available devices will appear in the device tree
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under that bus.
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Note that this is all done on a lazy basis, as needed, so until something is
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touched on PCI (eg: a call to pci_find_devices()) it will not be probed.
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PCI devices can appear in the device tree. If they do this serves to specify
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the driver to use for the device. In this case they will be bound at
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start-up.
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Sandbox
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-------
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With sandbox we need a device emulator for each device on the bus since there
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is no real PCI bus. This works by looking in the device tree node for a
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driver. For example:
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pci@1f,0 {
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compatible = "pci-generic";
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reg = <0xf800 0 0 0 0>;
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emul@1f,0 {
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compatible = "sandbox,swap-case";
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};
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};
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This means that there is a 'sandbox,swap-case' driver at that bus position.
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Note that the first cell in the 'reg' value is the bus/device/function. See
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PCI_BDF() for the encoding (it is also specified in the IEEE Std 1275-1994
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PCI bus binding document, v2.1)
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When this bus is scanned we will end up with something like this:
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`- * pci-controller @ 05c660c8, 0
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`- pci@1f,0 @ 05c661c8, 63488
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`- emul@1f,0 @ 05c662c8
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When accesses go to the pci@1f,0 device they are forwarded to its child, the
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emulator.
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