On Tue, 2021-12-28 at 10:15 +0100, Mauro Carvalho Chehab wrote:
Em Tue, 28 Dec 2021 09:21:23 +0100 Greg Kroah-Hartman gregkh@linuxfoundation.org escreveu:
On Mon, Dec 27, 2021 at 05:42:46PM +0100, Niklas Schnelle wrote:
--- a/drivers/pci/Kconfig +++ b/drivers/pci/Kconfig @@ -23,6 +23,17 @@ menuconfig PCI
if PCI
+config LEGACY_PCI
- bool "Enable support for legacy PCI devices"
- depends on HAVE_PCI
- help
This option enables support for legacy PCI devices. This includesPCI devices attached directly or via a bridge on a PCI Express bus.It also includes compatibility features on PCI Express devices whichmake use of legacy I/O spaces.This Kconfig doesn't seem what it is needed there, as this should be an arch-dependent feature, and not something that the poor user should be aware if a given architecture supports it or not. Also, the above will keep causing warnings or errors with randconfigs.
Also, the "depends on HAVE_CPI" is bogus, as PCI already depends on HAVE_PCI:
Ah yes you're right.
menuconfig PCI bool "PCI support" depends on HAVE_PCI help This option enables support for the PCI local bus, including support for PCI-X and the foundations for PCI Express support. Say 'Y' here unless you know what you are doing.
So, instead, I would expect that a new HAVE_xxx option would be added at arch/*/Kconfig, like:
config X86 ... select HAVE_PCI_DIRECT_IO
It would also make sense to document it at Documentation/features/.
I'll look into that, thanks.
All you really care about is the "legacy" I/O spaces here, this isn't tied to PCI specifically at all, right?
So why not just have a OLD_STYLE_IO config option or something like that, to show that it's the i/o functions we care about here, not PCI at all?
And maybe not call it "old" or "legacy" as time constantly goes forward, just describe it as it is, "DIRECT_IO"?
Agreed. HAVE_PCI_DIRECT_IO (or something similar) seems a more appropriate name for it.
Thanks, Mauro
Hmm, I might be missing something here but that sounds a lot like the HAS_IOPORT option added in patch 02.
We add both LEGACY_PCI and HAS_IOPORT to differentiate between two cases. HAS_IOPORT is for PC-style devices that are not on a PCI card while LEGACY_PCI is for PCI drivers that require port I/O. This includes pre-PCIe devices as well as PCIe devices which require features like I/O spaces. The "legacy" naming is comes from the PCIe spec which in section 2.1.1.2 says "PCI Express supports I/O Space for compatibility with legacy devices which require their use. Future revisions of this specification may deprecate the use of I/O Space."
These two separate config options allow us to compile without support for these legacy PCI devices even on a system where inb()/outb() and friends are required for some PC style devices and for example ACPI.