PCI: Set error response data when config read fails

When a PCI config read fails, most PCI host bridges fabricate ~0 data to
complete the CPU read.  But some host bridges do not; their drivers may
only return an error from the pci_ops.read() method.

In PCI_OP_READ() and PCI_USER_READ_CONFIG(), use PCI_SET_ERROR_RESPONSE()
to set the data value to indicate an error when pci_ops.read() fails.

This means the host bridge driver no longer needs to fabricate error data
when they detect errors.

This makes error response fabrication consistent and helps in removal of a
lot of repeated code.
Suggested-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/4188fc5465631ce0d472d1423de3d9fb2f09b8ff.1637243717.git.naveennaidu479@gmail.comSigned-off-by: Naveen Naidu <naveennaidu479@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Pali Rohár <pali@kernel.org>

drivers/pci/access.c

@@ -42,6 +42,9 @@ int noinline pci_bus_read_config_##size \
 	if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;	\
 	pci_lock_config(flags);						\
 	res = bus->ops->read(bus, devfn, pos, len, &data);		\
+	if (res)							\
+		PCI_SET_ERROR_RESPONSE(value);				\
+	else								\
 		*value = (type)data;					\
 	pci_unlock_config(flags);					\
 	return res;							\
@@ -228,6 +231,9 @@ int pci_user_read_config_##size						\
 	ret = dev->bus->ops->read(dev->bus, dev->devfn,			\
 					pos, sizeof(type), &data);	\
 	raw_spin_unlock_irq(&pci_lock);				\
+	if (ret)							\
+		PCI_SET_ERROR_RESPONSE(val);				\
+	else								\
 		*val = (type)data;					\
 	return pcibios_err_to_errno(ret);				\
 }									\