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SubjectTesting for extended PCI config space

It's kind of tricky to figure out whether we can access the extended
config space or not. Given that nobody checks the return value from
pci_read_config_*(), I don't know whether we'll be able to persuade them
to check pdev->cfg_size or not, but we can at least try to get it right.

/**
* pci_cfg_space_size - get the configuration space size of the PCI device.
*
* Regular PCI devices have 256 bytes, but PCI-X 2 and PCI Express devices
* have 4096 bytes. Even if the device is capable, that doesn't mean we can
* access it. Maybe we don't have a way to generate extended config space
* accesses, or the device is behind a reverse Express bridge. So we try
* reading the dword at 0x100 which must either be 0 or a valid extended
* capability header.
*/
static int pci_cfg_space_size(struct pci_dev *dev)
{
int pos;
u32 status;

pos = pci_find_capability(dev, PCI_CAP_ID_EXP);
if (!pos) {
pos = pci_find_capability(dev, PCI_CAP_ID_PCIX);
if (!pos)
goto fail;

pci_read_config_dword(dev, pos + PCI_X_STATUS, &status);
if (!(status & (PCI_X_STATUS_266MHZ | PCI_X_STATUS_533MHZ)))
goto fail;
}

if (pci_read_config_dword(dev, 256, &status) != PCIBIOS_SUCCESSFUL)
goto fail;
if (status == 0xffffffff)
goto fail;

return PCI_CFG_SPACE_EXP_SIZE;

fail:
return PCI_CFG_SPACE_SIZE;
}


--
"Next the statesmen will invent cheap lies, putting the blame upon
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince
himself that the war is just, and will thank God for the better sleep
he enjoys after this process of grotesque self-deception." -- Mark Twain
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