Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled

[Connor Davis <connojdavis@xxxxxxxxx>]

On 5/17/21 3:32 AM, Jan Beulich wrote:
> On 14.05.2021 02:56, Connor Davis wrote:
> > Check if the debug capability is enabled in early_xdbc_parse_parameter,
> > and if it is, return with an error. This avoids collisions with whatever
> > enabled the DbC prior to linux starting.
> Doesn't this go too far and prevent use even if firmware (perhaps
> mistakenly) left it enabled?
>
> Jan
Yes, but how is one supposed to distinguish the broken firmware and 
non-broken
firmware cases?

> > Signed-off-by: Connor Davis <connojdavis@xxxxxxxxx>
> > ---
> >   drivers/usb/early/xhci-dbc.c | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
> > index be4ecbabdd58..ca67fddc2d36 100644
> > --- a/drivers/usb/early/xhci-dbc.c
> > +++ b/drivers/usb/early/xhci-dbc.c
> > @@ -642,6 +642,16 @@ int __init early_xdbc_parse_parameter(char *s)
> >         }
> >         xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
> >   
> > +	if (readl(&xdbc.xdbc_reg->control) & CTRL_DBC_ENABLE) {
> > +               pr_notice("xhci debug capability already in use\n");
> > +               early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> > +               xdbc.xdbc_reg = NULL;
> > +               xdbc.xhci_base = NULL;
> > +               xdbc.xhci_length = 0;
> > +
> > +               return -ENODEV;
> > +       }
> > +
> >         return 0;
> >   }
> >   
Thanks,

Connor