Hello,
> The only platform without these aforementioned defines is Alpha, which is
> conventional PCI only and cannot have ReBAR. So this guard removes dead
> sysfs code on platforms where it can never be executed.
Having a closer look:
resource_resize_attr_is_visible()
pci_rebar_get_current_size() <- returns -ENOTSUPP, so is_visible
callback returns 0
pci_rebar_find_pos()
pos = pdev->rebar_cap <- set to 0 on a conventional PCI
if (!pos)
return -ENOTSUPP <- no ReBAR support
The pdev->rebar_cap is set during PCI enumeration:
pci_init_capabilities()
pci_rebar_init()
pdev->rebar_cap = pci_find_ext_capability()
pci_find_next_ext_capability()
if (dev->cfg_size <= PCI_CFG_SPACE_SIZE)
return 0; <- dev->cfg_size set to 256 here for
conventional PCI
The PCI_CFG_SPACE_SIZE is 256 here.
When the platform has support for PCI Express, the dev->cfg_size is then
set to 4096. On an architecture that supports conventional PCI only (such
as Alpha), the pdev->rebar_cap will be set to 0, the is_visible callback
will then return 0, and the resize sysfs attribute is never created, as
such, the __resource_resize_store() callback will never be executed.
To make the connetion here to the #ifdef guards:
For the pci_rebar_get_current_size() to return >= 0, the device needs
PCI Express and extended configuration space support. As of today,
every architecture with PCI Express support defines HAVE_PCI_MMAP or
ARCH_GENERIC_PCI_MMAP_RESOURCE.
I hope the reasoning here works.
Thank you!
Krzysztof
