On Mon, Mar 08, 2021 at 12:52:12PM -0600, Bjorn Helgaas wrote: > On Mon, Mar 08, 2021 at 02:20:16PM +0200, Andy Shevchenko wrote: > > From: Jonathan Yong <jonathan.yong@xxxxxxxxx> > > > > There is already one and at least one more user is coming which > > requires an access to Primary to Sideband bridge (P2SB) in order to > > get IO or MMIO bar hidden by BIOS. Create a library to access P2SB > > for x86 devices. > > Can you include a spec reference? I'm not sure I have a public link to the spec. It's the 100 Series PCH [1]. The document number to look for is 546955 [2] and there actually a bit of information about this. > I'm trying to figure out why this > belongs in drivers/pci/. It looks very device-specific. Because it's all about access to PCI configuration spaces of the (hidden) devices. [1]: https://ark.intel.com/content/www/us/en/ark/products/series/98456/intel-100-series-desktop-chipsets.html [2]: https://medium.com/@jacksonchen_43335/bios-gpio-p2sb-70e9b829b403 ... > > +config PCI_P2SB > > + bool "Primary to Sideband (P2SB) bridge access support" > > + depends on PCI && X86 > > + help > > + The Primary to Sideband bridge is an interface to some PCI > > + devices connected through it. In particular, SPI NOR > > + controller in Intel Apollo Lake SoC is one of such devices. > > This doesn't sound like a "bridge". If it's a bridge, what's on the > primary (upstream) side? What's on the secondary side? What > resources are passed through the bridge, i.e., what transactions does > it transfer from one side to the other? It's a confusion terminology here. It's a Bridge according to the spec, but it is *not* a PCI Bridge as you may had a first impression. ... > > + /* Unhide the P2SB device */ > > + pci_bus_write_config_byte(bus, df, P2SBC_HIDE_BYTE, 0); > > + > > + /* Read the first BAR of the device in question */ > > + __pci_bus_read_base(bus, devfn, pci_bar_unknown, mem, PCI_BASE_ADDRESS_0, true); > > I don't get this. Apparently this normally hidden device is consuming > PCI address space. The PCI core needs to know about this. If it > doesn't, the PCI core may assign this space to another device. Right, it returns all 1:s to any request so PCI core *thinks* it's plugged off (like D3cold or so). > > + /* Hide the P2SB device */ > > + pci_bus_write_config_byte(bus, df, P2SBC_HIDE_BYTE, P2SBC_HIDE_BIT); -- With Best Regards, Andy Shevchenko
