[Linux-kernel-mentees] [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
bp at alien8.de
Sun Aug 2 18:46:48 UTC 2020
On Sun, Aug 02, 2020 at 07:28:00PM +0200, Saheed Bolarinwa wrote:
> Because the value ~0 has a meaning to some drivers and only
No, ~0 means that the PCI read failed. For *every* PCI device I know.
Here's me reading from 0xf0 offset of my hostbridge:
# setpci -s 00:00.0 0xf0.l
That device doesn't have extended config space, so the last valid byte
is 0xff. Let's read beyond that:
# setpci -s 00:00.0 0x100.l
> Again, only the drivers can determine if ~0 is a valid value. This
> information is not available inside pci_config_read*().
Of course it is.
*every* change you've done in 6/17 - this is the only patch I have
received - checks for == ~0. So that check can just as well be moved
Here's how one could do it:
#define PCI_OP_READ(size, type, len) \
int noinline pci_bus_read_config_##size \
(struct pci_bus *bus, unsigned int devfn, int pos, type *value) \
int res; \
unsigned long flags; \
u32 data = 0; \
if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER; \
res = bus->ops->read(bus, devfn, pos, len, &data); \
/* Check we actually read something which is not all 1s.*/
if (data == ~0)
*value = (type)data; \
return res; \
Also, I'd prefer a function to *not* return void but return either
an error or success. In the success case, the @value argument can be
consumed by the caller and otherwise not.
In any case, that change is a step in the wrong direction and I don't
like it, sorry.
More information about the Linux-kernel-mentees