[+cc Pali]
On Mon, Oct 11, 2021 at 05:05:54PM -0500, Rob Herring wrote:
> On Mon, Oct 11, 2021 at 11:08:32PM +0530, Naveen Naidu wrote:
> > An MMIO read from a PCI device that doesn't exist or doesn't respond
> > causes a PCI error. There's no real data to return to satisfy the
> > CPU read, so most hardware fabricates ~0 data.
> >
> > Use SET_PCI_ERROR_RESPONSE() to set the error response and
> > RESPONSE_IS_PCI_ERROR() to check the error response during hardware
> > read.
> >
> > These definitions make error checks consistent and easier to find.
> >
> > Signed-off-by: Naveen Naidu <naveennaidu479@xxxxxxxxx>
> > ---
> > drivers/pci/access.c | 22 +++++++++++-----------
> > 1 file changed, 11 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> > index 46935695cfb9..e1954bbbd137 100644
> > --- a/drivers/pci/access.c
> > +++ b/drivers/pci/access.c
> > @@ -81,7 +81,7 @@ int pci_generic_config_read(struct pci_bus *bus, unsigned int devfn,
> >
> > addr = bus->ops->map_bus(bus, devfn, where);
> > if (!addr) {
> > - *val = ~0;
> > + SET_PCI_ERROR_RESPONSE(val);
>
> This to me doesn't look like kernel style. I'd rather see a define
> replace just '~0', but I defer to Bjorn.
>
> > return PCIBIOS_DEVICE_NOT_FOUND;
>
> Neither does this using custom error codes rather than standard Linux
> errno. I point this out as I that's were I'd start with the config
> accessors. Though there are lots of occurrences so we'd need a way to do
> this in manageable steps.
I would love to see PCIBIOS_* confined to arch/x86 and everywhere else
using standard Linux error codes. That's probably a lot of work, but
Naveen has a lot of energy :)
> Can't we make PCI_OP_READ and PCI_USER_READ_CONFIG set the data value
> and delete the drivers all doing this? Then we have 2 copies (in source)
> rather than the many this series modifies. Though I'm not sure if there
> are other cases of calling pci_bus.ops.read() which expect to get ~0.
That does seem like a really good idea.
Bjorn
