Hello all,
I'm trying to provide hot-swap support for GPU devices, specifically
headless GPUs. The native PCIe hotplug drivers prevent this explicitly
with the following (referencing pciehp but the same can be found in shpchp):
int pciehp_unconfigure_device(struct slot *p_slot)
{
...
for (j = 0; j < 8; j++) {
...
if ((temp->class >> 16) == PCI_BASE_CLASS_DISPLAY) {
ctrl_err(ctrl, "Cannot remove display device %s\n",
pci_name(temp));
pci_dev_put(temp);
continue;
}
if (temp->hdr_type == PCI_HEADER_TYPE_BRIDGE && presence) {
pci_read_config_byte(temp, PCI_BRIDGE_CONTROL, &bctl);
if (bctl & PCI_BRIDGE_CTL_VGA) {
ctrl_err(ctrl,
"Cannot remove display device %s\n",
pci_name(temp));
pci_dev_put(temp);
continue;
}
}
...
}
A similar check is made in pciehp_configure_device() to prevent
hot-adding a display device.
Why is this check needed? Is it to prevent a user from hot-removing a
graphics card that is driving their display? If so, this seems like a
heavy hammer to protect against a user-requested (albeit probably naive)
action. I've tested hotplug of GPU's with a patch to remove this check
and it appears to work without negative side effects. Is there something
I'm missing about this check?
Also, if these checks are indeed necessary I believe there may be a bug
in pciehp_unconfigure_device(). By not setting an rc value if the
display adapter condition is met, the function will return successfully
without properly unconfiguring the device. Then remove_board() would
end up powering the slot off anyway. There is a similar but less severe
issue with pciehp_configure_device() in the hot-add scenario.
Thanks for the help.
Cheers,
Praveen
--
Praveen Kalamegham
praveen@xxxxxxxxxx
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