Re: [PATCH v2 2/3] MIPS: cm/cpc: export some missing symbols to be able to use them from driver code

Bjorn Helgaas
2021-10-29T18:49:54Z

On Fri, Oct 29, 2021 at 07:28:47AM +0200, Sergio Paracuellos wrote:
> On Thu, Oct 28, 2021 at 10:47 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Thu, Oct 28, 2021 at 11:59:17AM +0200, Sergio Paracuellos wrote:
> > > On Thu, Oct 28, 2021 at 11:34 AM Sergio Paracuellos
> > > <sergio.paracuellos@gmail.com> wrote:
> > > > On Thu, Oct 28, 2021 at 11:24 AM Thomas Bogendoerfer
> > > > <tsbogend@alpha.franken.de> wrote:
> > > > > On Thu, Oct 28, 2021 at 06:11:18AM +0200, Sergio Paracuellos wrote:
> > > > > > On Thu, Oct 28, 2021 at 6:05 AM Yanteng Si <siyanteng01@gmail.com> wrote:
> > > > > > >
> > > > > > > Since commit 2bdd5238e756 ("PCI: mt7621: Add MediaTek MT7621 PCIe host controller driver")
> > > > > > > the MT7621 PCIe host controller driver is built as a module but modpost complains once these
> > > > > > > drivers become modules.
> > > > > > >
> > > > > > > ERROR: modpost: "mips_cm_unlock_other" [drivers/pci/controller/pcie-mt7621.ko] undefined!
> > > > > > > ERROR: modpost: "mips_cpc_base" [drivers/pci/controller/pcie-mt7621.ko] undefined!
> > > > > > > ERROR: modpost: "mips_cm_lock_other" [drivers/pci/controller/pcie-mt7621.ko] undefined!
> > > > > > > ERROR: modpost: "mips_cm_is64" [drivers/pci/controller/pcie-mt7621.ko] undefined!
> > > > > > > ERROR: modpost: "mips_gcr_base" [drivers/pci/controller/pcie-mt7621.ko] undefined!
> > > > > > >
> > > > > > > Let's just export them.
> > > > > > >
> > > > > > > Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
> > > > > > > ---
> > > > > > > arch/mips/kernel/mips-cm.c | 5 +++++
> > > > > > > arch/mips/kernel/mips-cpc.c | 1 +
> > > > > > > 2 files changed, 6 insertions(+)
> > > > > > >
> > > > > >
> > > > > > Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
> > > > >
> > > > > could we instead make the pcie-mt761 driver non modular ? Exporting
> > > > > all MIPS specific stuff for just making an essential driver modular
> > > > > doesn't IMHO make much sense.
> > > >
> > > > The driver is modular because I have been advised other times that new
> > > > drivers should be able to be compiled as modules and we should avoid
> > > > using 'bool' in Kconfig for new drivers. That's the only reason. I am
> > > > also always including as 'y' the driver since for me not having pci in
> > > > my boards has no sense... I am ok in changing Kconfig to be 'bool'
> > > > instead of 'tristate', but I don't know what should be the correct
> > > > thing to do in this case. Thoughts?
> > >
> > > I guess we also want the driver to at least be compile tested in
> > > 'allmodconfig' and other similars...15692a80d949
> >
> > Sounds like the systems that actually use this driver require it to be
> > built-in, and the only benefit of exporting these symbols is that we
> > would get better compile test coverage.
> >
> > If that's the case, I agree that it's better to just make it
> > non-modular.
>
> I agree and that was my reasoning for sending a patch to also convert
> to bool the phy driver that this PCIe controller uses. When the pull
> request was sent from Vinod to Greg, Greg refused to take it because
> of that commit and the commit was reverted and a new pull request was
> sent including this revert. This is commit 15692a80d949 ("phy: Revert
> "phy: ralink: Kconfig: convert mt7621-pci-phy into 'bool'""). Because
> of this I also changed the PCIe controller Kconfig from bool to
> tristate when I sent v3 of the series which at the end were the ones
> that was finally taken. There are also other ralink related symbols
> that have been exported to allow to compile other drivers as a
> modules, like the watchdog. See the commit fef532ea0cd8 ("MIPS:
> ralink: export rt_sysc_membase for rt2880_wdt.c"). So, as I said, I
> agree and I am using the driver as if it were a bool and also ralink
> systems normally require all drivers built-in, but I think we have to
> take into account also the "historical facts" here. In any case,
> Bjorn, let me know if you want me to send whatever patch might be
> needed.

I didn't see the conversation with Greg, so I don't know the whole
story.

For pcie-mt7621.c, it looks like the only problem is
setup_cm_memory_region(), which does a little coherency-related stuff.
If we could move that to arch/mips, we could still make this tristate.

One way might be to implement a pcibios_root_bridge_prepare() for mips
and put the setup_cm_memory_region() stuff in there. It's not *ideal*
because that's a strong/weak function arrangement that doesn't allow
for multiple host bridges, but that's probably not an issue here.

If we can't do that, I think making it bool is probably the right
answer, but it would be worth a brief comment in the commit log to
explain the issue.

Bjorn