Hi, Bjorn,
On Wed, Jun 1, 2022 at 7:14 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Sat, Apr 30, 2022 at 04:48:43PM +0800, Huacai Chen wrote:
> > On LS2K/LS7A, some unexisting devices don't return 0xffffffff when
> > scanning. This is a hardware flaw but we can only avoid it by software
> > now.
>
> s/unexisting/non-existant/ (many occurrences: subject line, commit
> log, comments below)
OK, thanks.
>
> What happens in other situations that normally cause Unsupported
> Request or similar errors? For example, memory reads/writes to a
> device in D3hot should cause an Unsupported Request error. I'm
> wondering whether other error handling assumptions might be broken
> on LS2K/LS7A.
Hardware engineers told me that the problem is due to pin
multiplexing, under some configurations, a PCI device is unusable but
the read request doesn't return 0xffffffff.
>
> > Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > ---
> > drivers/pci/controller/pci-loongson.c | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
> > index adbfa4a2330f..48316daa1f23 100644
> > --- a/drivers/pci/controller/pci-loongson.c
> > +++ b/drivers/pci/controller/pci-loongson.c
> > @@ -138,6 +138,8 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus, unsigned int devf
> > int where)
> > {
> > unsigned char busnum = bus->number;
> > + unsigned int device = PCI_SLOT(devfn);
> > + unsigned int function = PCI_FUNC(devfn);
> > struct loongson_pci *priv = pci_bus_to_loongson_pci(bus);
> >
> > if (pci_is_root_bus(bus))
> > @@ -147,8 +149,13 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus, unsigned int devf
> > * Do not read more than one device on the bus other than
> > * the host bus. For our hardware the root bus is always bus 0.
> > */
> > - if (priv->data->flags & FLAG_DEV_FIX &&
> > - !pci_is_root_bus(bus) && PCI_SLOT(devfn) > 0)
> > + if ((priv->data->flags & FLAG_DEV_FIX) && bus->self) {
> > + if (!pci_is_root_bus(bus) && (device > 0))
> > + return NULL;
> > + }
> > +
> > + /* Don't access unexisting devices */
> > + if (pci_is_root_bus(bus) && (device >= 9 && device <= 20 && function > 0))
>
> Yuck. This is pretty nasty magic. If this is something that might be
> fixed in future versions of the hardware, maybe you should factor this
> out into a function pointer in loongson_pci_data or something.
OK, seems providing a pdev_is_existant() is better.
Huacai
>
> > return NULL;
> >
> > /* CFG0 can only access standard space */
> > --
> > 2.27.0
> >
