Re: [PATCH v2 3/4] usb: dbgp: Fix return values for reset prep and startup

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 5/13/21 8:56 PM, Connor Davis wrote:
> Callers of dbgp_reset_prep treat a 0 return value as "stop using
> the debug port", which means they don't make any subsequent calls to
> dbgp_reset_prep or dbgp_external_startup.
>
> To ensure the callers' interpretation is correct, first return -EPERM
> from xen_dbgp_op if !xen_initial_domain(). This ensures that
> both xen_dbgp_reset_prep and xen_dbgp_external_startup return 0
> iff the PHYSDEVOP_DBGP_RESET_{PREPARE,DONE} hypercalls succeed. Also
> update xen_dbgp_reset_prep and xen_dbgp_external_startup to return
> -EPERM when !CONFIG_XEN_DOM0 for consistency.
>
> Next, return nonzero from dbgp_reset_prep if xen_dbgp_reset_prep returns
> 0. The nonzero value ensures that callers of dbgp_reset_prep will
> subsequently call dbgp_external_startup when it is safe to do so.
>
> Also invert the return values from dbgp_external_startup for
> consistency with dbgp_reset_prep (this inversion has no functional
> change since no callers actually check the value).
>
> Signed-off-by: Connor Davis <connojdavis@xxxxxxxxx>


For Xen bits:


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>


For the rest it seems to me that error code passing could be improved: if it's 
0 or 1 it should be bool. Or pass actual error code, with zero for no-error 
case, such as ...


> ---
>  drivers/usb/early/ehci-dbgp.c |  9 ++++++---
>  drivers/xen/dbgp.c            |  2 +-
>  include/linux/usb/ehci-dbgp.h | 14 +++++++++-----
>  3 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/usb/early/ehci-dbgp.c b/drivers/usb/early/ehci-dbgp.c
> index 45b42d8f6453..ff993d330c01 100644
> --- a/drivers/usb/early/ehci-dbgp.c
> +++ b/drivers/usb/early/ehci-dbgp.c
> @@ -970,8 +970,8 @@ int dbgp_reset_prep(struct usb_hcd *hcd)
>       int ret = xen_dbgp_reset_prep(hcd);
>       u32 ctrl;
>  
> -     if (ret)
> -             return ret;
> +     if (!ret)
> +             return 1;


... here or ...


>  
>       dbgp_not_safe = 1;
>       if (!ehci_debug)
> @@ -995,7 +995,10 @@ EXPORT_SYMBOL_GPL(dbgp_reset_prep);
>  
>  int dbgp_external_startup(struct usb_hcd *hcd)
>  {
> -     return xen_dbgp_external_startup(hcd) ?: _dbgp_external_startup();
> +     if (!xen_dbgp_external_startup(hcd))
> +             return 1;


... here.


-boris