Em Wed, 29 Dec 2021 12:45:38 +0100 Niklas Schnelle <schnelle@xxxxxxxxxxxxx> escreveu: > On Tue, 2021-12-28 at 18:12 +0100, Mauro Carvalho Chehab wrote: > > Em Tue, 28 Dec 2021 16:06:44 +0100 > > Niklas Schnelle <schnelle@xxxxxxxxxxxxx> escreveu: > > > > (on a side note: the c/c list of this patch is too long. I would try to > > avoid using a too long list, as otherwise this e-mail may end being rejected > > by mail servers) > > > > > On Tue, 2021-12-28 at 13:54 +0100, Mauro Carvalho Chehab wrote: > > > > > > > ---8<--- > > > > > > > > > > > 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. > > > > > > > > I didn't look at the other patches on this series, but why it is needed > > > > to deal with them on a separate way? Won't "PCI" and "HAS_IOPORT" be enough? > > > > > > > > I mean, are there any architecture where HAVE_PCI=y and HAS_IOPORT=y > > > > where LEGACY_PCI shall be "n"? > > > > > > In the current patch set LEGACY_PCI is not currently selected by > > > architectures, though of course it could be if we know that an > > > architecture requires it. We should probably also set it in any > > > defconfig that has devices depending on it so as not to break these. > > > > > > Other than that it would be set during kernel configuration if one > > > wants/needs support for legacy PCI devices. For testing I ran with > > > HAVE_PCI=y, HAS_IOPORT=y and LEGACY_PCI=n on both my local Ryzen 3990X > > > based workstation and Raspberry Pi 4 (DT). I guess at the moment it > > > would make most sense for special configs such as those tailored for > > > vitualization guets but in the end that would be something for > > > distributions to decide. > > > > IMO, it makes sense to have a "default y" there, as on systems that > > support I/O space, disabling it will just randomly disable some drivers > > that could be required by some hardware. I won't doubt that some of > > those could be ported from using inb/outb to use, instead, readb/writeb. > > Makes sense, if these get more legacy over time we can always change > the default. This would also mean we don't need to change defconfigs > that include legacy PCI devices. Yes. > > > > > Arnd described the options here: > > > https://lore.kernel.org/lkml/CAK8P3a3HHeP+Gw_k2P7Qtig0OmErf0HN30G22+qHic_uZTh11Q@xxxxxxxxxxxxxx/ > > > > Based on Arnd's description, LEGACY_PCI should depend on HAS_IOPORT. > > This is missing on patch 1. You should probably reorder your patch > > series to first create HAS_IOPORT and then add LEGACY_PCI with > > depends on, as otherwise it may cause randconfig build issues > > at robots and/or git bisect. > > > > I would also suggest to first introduce such change and then send > > a per-subsystem LEGACY_PCI patch, as it would be a lot easier for > > maintainers to review. > > Playing around with the reordering I think it might make sense to > introduce HAS_IOPORT in patch 01, then LEGACY_PCI in patch 02 and then > add dependencies for both on a per subsystem basis. I think it would be > overkill to have two series of per subsystem patches. Makes sense to me. Yeah, a single series should work. > > > > > > > > > > > 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." > > > > > > > > I would still avoid calling it LEGACY_PCI, as this sounds too generic. > > > > > > > > I didn't read the PCI/PCIe specs, but I suspect that are a lot more > > > > features that were/will be deprecated on PCI specs as time goes by. > > > > > > > > So, I would, instead, use something like PCI_LEGACY_IO_SPACE or > > > > HAVE_PCI_LEGACY_IO_SPACE, in order to let it clear what "legacy" > > > > means. > > > > > > Hmm, I'd like to hear Bjorn's opinion on this. Personally I feel like > > > LEGACY_PCI is pretty clear since most devices are either pre-PCIe > > > devices or a compatibility feature allowing drivers for a pre-PCIe > > > device to work with a PCIe device. > > > > That's the main point: it is *not* disabling pre-PCIe devices or > > even legacy PCI drivers. It just disables a random set of drivers just > > because they use inb/outb instead of readb/writeb. It keeps several pure > > PCI drivers selected, and disables some PCIe for no real reason. > > That is not intentional. The dependencies are certainly not perfect yet > which is one of the reasons this is still an RFC. I hope getting these > right will be a lot easier if we do both LEGACY_PCI and HAS_IOPORT > dependency selection on a per subsystem basis. Ok. > > > > Just to give one example, this symbol: > > > > > diff --git a/drivers/media/cec/platform/Kconfig b/drivers/media/cec/platform/Kconfig > > > index b672d3142eb7..5e92ece5b104 100644 > > > --- a/drivers/media/cec/platform/Kconfig > > > +++ b/drivers/media/cec/platform/Kconfig > > > @@ -100,7 +100,7 @@ config CEC_TEGRA > > > config CEC_SECO > > > tristate "SECO Boards HDMI CEC driver" > > > depends on (X86 || IA64) || COMPILE_TEST > > > - depends on PCI && DMI > > > + depends on LEGACY_PCI && DMI > > > select CEC_CORE > > > select CEC_NOTIFIER > > > help > > > > Disables HDMI CEC support on some Intel motherboards. > > Any distro meant to run on generic hardware should keep it selected. > > As far as I can see this one actually uses a hardcoded I/O port numbers > and googling it looks like it's an on-board device on the UDOO x86 > board. I guess that should indeed just be > "depends on PCI && DMI && HAS_IOPORT". Agreed. > > > > > I can see some value of a "PCI_LEGACY" option to disable all > > non-PCIe drivers, but this is not the case here. > > > > Thanks, > > Mauro > > Ok, I think we definitely need to work on getting the dependencies > right. Yes. > I do think we agree that once done correctly there is value in > such an option independent of HAS_IOPORT only gating inb() etc uses. Personally, I don't see much value on a Kconfig var for legacy PCI I/O space. From maintenance PoV, bots won't be triggered if someone use HAS_IOPORT instead of the PCI specific one - or vice-versa. So, we could end having a mix of both at the wrong places, in long term. Also, assuming that PCIe hardware will some day abandon support for "legacy" PCI I/O space, I guess some runtime logic would be needed, in order to work with both kinds of PCIe controllers. So, having a Kconfig option won't help much, IMO. So, my personal preference would be to have just one Kconfig var, but I'm ok if the PCI maintainers decide otherwise. Thanks, Mauro
