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

["Marek Behún" <kabel@kernel.org>]

On Wed, 8 Sep 2021 09:06:28 +0800
Bin Meng <bmeng.cn@gmail.com> wrote:

> On Wed, Sep 8, 2021 at 12:07 AM Marek Behún <marek.behun@nic.cz>
> wrote:
> >
> > From: Pali Rohár <pali@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@kernel.org>
> > Signed-off-by: Marek Behún <marek.behun@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.

Marek