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Diffstat (limited to 'docs/specs/pci-testdev.rst')
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diff --git a/docs/specs/pci-testdev.rst b/docs/specs/pci-testdev.rst new file mode 100644 index 0000000000..4b6d36543b --- /dev/null +++ b/docs/specs/pci-testdev.rst @@ -0,0 +1,39 @@ +==================== +QEMU PCI test device +==================== + +``pci-testdev`` is a device used for testing low level IO. + +The device implements up to three BARs: BAR0, BAR1 and BAR2. +Each of BAR 0+1 can be memory or IO. Guests must detect +BAR types and act accordingly. + +BAR 0+1 size is up to 4K bytes each. +BAR 0+1 starts with the following header: + +.. code-block:: c + + typedef struct PCITestDevHdr { + uint8_t test; /* write-only, starts a given test number */ + uint8_t width_type; /* + * read-only, type and width of access for a given test. + * 1,2,4 for byte,word or long write. + * any other value if test not supported on this BAR + */ + uint8_t pad0[2]; + uint32_t offset; /* read-only, offset in this BAR for a given test */ + uint32_t data; /* read-only, data to use for a given test */ + uint32_t count; /* for debugging. number of writes detected. */ + uint8_t name[]; /* for debugging. 0-terminated ASCII string. */ + } PCITestDevHdr; + +All registers are little endian. + +The device is expected to always implement tests 0 to N on each BAR, and to add new +tests with higher numbers. In this way a guest can scan test numbers until it +detects an access type that it does not support on this BAR, then stop. + +BAR2 is a 64bit memory BAR, without backing storage. It is disabled +by default and can be enabled using the ``membar=<size>`` property. This +can be used to test whether guests handle PCI BARs of a specific +(possibly quite large) size correctly. |