Subject: Re: [PATCH 2/2] powerpc/eeh: Use pcie_reset_state_t type in function arguments

From: Bjorn Helgaas <[email-masked]>
Date: Thu, 24 Mar 2022 17:09:08 -0500

On Thu, Mar 10, 2022 at 09:51:13AM +0100, Christophe Leroy wrote:
> Le 13/07/2021 à 02:25, Krzysztof Wilczyński a écrit :
> > The pcie_reset_state_t type has been introduced in the commit
> > f7bdd12d234d ("pci: New PCI-E reset API") along with the enum
> > pcie_reset_state, but it has never been used for anything else
> > other than to define the members of the enumeration set in the
> > enum pcie_reset_state.
> > 
> > Thus, replace the direct use of enum pcie_reset_state in function
> > arguments and replace it with pcie_reset_state_t type so that the
> > argument type matches the type used in enum pcie_reset_state.
> > 
> > Signed-off-by: Krzysztof Wilczyński <[email-masked]>
> 
> I don't understand the purpose of this change. Does any tool like
> sparse of so reports an error here ?
> 
> My feeling is that by doing this you loose the added value of using
> an enumerate.
> 
> state is used in a switch/case, that's exactly what we expect from
> an enum.

I think this is true: in the patch below, we remove use of "enum
pcie_reset_state", so the compiler no longer knows that "state" is an
enum, and it cannot verify that "state" has a legal value in the
switch statement.  And at least with "gcc -Wall", it looks like it
*does* complain in that case.

Whether that value is worthwhile, I don't know.  AFAICT this is the
only place that uses "state", so there's not *much* value.

If we did apply the patch below, I think we could probably make "enum
pcie_reset_state" an anonymous enum instead, like the enum for
pci_channel_state_t.

But let's back up for a minute.  This is only used in the
pci_set_pcie_reset_state() path, and that's only used by three
drivers: cxl, genwqe, and ipr, and obviously only on powerpc, since
that's the only arch that implements pcibios_set_pcie_reset_state().

What's special about them?  Why do they need this and no other drivers
do?  And why only on powerpc?

I wonder if that powerpc functionality could be implemented in some
way that's more integrated into the PCI core reset and error handling
framework.

> > ---
> >   arch/powerpc/kernel/eeh.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
> > index 3bbdcc86d01b..15485abb89ff 100644
> > --- a/arch/powerpc/kernel/eeh.c
> > +++ b/arch/powerpc/kernel/eeh.c
> > @@ -714,7 +714,7 @@ static void eeh_restore_dev_state(struct eeh_dev *edev, void *userdata)
> >    * Return value:
> >    * 	0 if success
> >    */
> > -int pcibios_set_pcie_reset_state(struct pci_dev *dev, enum pcie_reset_state state)
> > +int pcibios_set_pcie_reset_state(struct pci_dev *dev, pcie_reset_state_t state)
> >   {
> >   	struct eeh_dev *edev = pci_dev_to_eeh_dev(dev);
> >   	struct eeh_pe *pe = eeh_dev_to_pe(edev);