[PATCH u-boot] dm: pci: Fix handling of errors when scanning device

[Bin Meng]

On Wed, Sep 8, 2021 at 8:02 PM Marek Behún <kabel at kernel.org> wrote:
>
> On Wed, 8 Sep 2021 09:06:28 +0800
> Bin Meng <bmeng.cn at gmail.com> wrote:
>
> > On Wed, Sep 8, 2021 at 12:07 AM Marek Behún <marek.behun at nic.cz>
> > wrote:
> > >
> > > From: Pali Rohár <pali at kernel.org>
> > >
> > > Some PCIe controller's read_config() method support indicating error
> > > directly via return value, but some cannot distinguish all-ones (or
> > > all-zeros) read response from an error.
> > >
> > > The current code in pci_bind_bus_devices() interprets all-ones /
> > > all-zeros in PCI_VENDOR_ID register as "nothing connected", and
> > > continues the cycle, but an error returned via return value breaks
> > > the cycle.
> > >
> > > This is wrong for the PCIe controllers which return this error via
> > > return value.
> > >
> > > Handle all errors when reading PCI_VENDOR_ID the same way.
> > >
> > > This fixes enumeration of PCI devices for example when there is a
> > > PCI bridge connected behind another PCI bridge and not all ports are
> > > connected to a device, and the controller (for example Aardvark)
> > > translates the UR error (Unsupported Request) as -EOPNOTSUPP.
> > >
> > > Signed-off-by: Pali Rohár <pali at kernel.org>
> > > Signed-off-by: Marek Behún <marek.behun at nic.cz>
> > > ---
> > >  drivers/pci/pci-uclass.c | 9 +--------
> > >  1 file changed, 1 insertion(+), 8 deletions(-)
> > >
> >
> > Is it possible to update these PCI controller drivers to fill in
> > vendor id to all zeros when there is an errror?
>
> It is, but we think it is wrong. If the PCI controller supports
> reporting errors, they should be propagated.
>
> What we might want to change in those controller drivers, though, is
> error numbers, so that they are the same for each controller. For
> example Unsupported Request should be always translated to EOPNOTSUPP.

So if it is a real error that for some reason the controller cannot
read the configuration space, we should abort instead of continue
looping.

Not sure what is the best approach though.

FWIW,
Reviewed-by: Bin Meng <bmeng.cn at gmail.com>