[v1] of: property: Don't retry device_link_add() upon failure

When of_link_to_phandle() was implemented initially, there was no way to
tell if device_link_add() was failing because the supplier device hasn't
been parsed yet, hasn't been added yet, the links were creating a cycle,
etc. Some of these were transient errors that'd go away at a later
point.

However, with the current set of improved checks, if device_link_add()
fails, it'll only be for permanent errors like cycles or out-of-memory
errors.

Also, with the addition of DL_FLAG_SYNC_STATE_ONLY flag [1] to device
links, all the valid dependency cycles due to "proxy" device links
(needed for correctness of sync_state() device callback) will never fail
device_link_add() due to cycles.

So, continuing to retry failing device links (by returning -EAGAIN) is
no longer useful. At worst, it prevents platforms from setting
fw_devlink=on (or better) because it prevents proper boot up. So, let's
not do that anymore.

[1] - https://lore.kernel.org/lkml/20191028220027.251605-1-saravanak@google.com/
Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 drivers/of/property.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Thu, 2020-04-16 at 13:58 -0700, Saravana Kannan wrote:
> When of_link_to_phandle() was implemented initially, there was no way to
> tell if device_link_add() was failing because the supplier device hasn't
> been parsed yet, hasn't been added yet, the links were creating a cycle,
> etc. Some of these were transient errors that'd go away at a later
> point.
> 
> However, with the current set of improved checks, if device_link_add()
> fails, it'll only be for permanent errors like cycles or out-of-memory
> errors.
> 
> Also, with the addition of DL_FLAG_SYNC_STATE_ONLY flag [1] to device
> links, all the valid dependency cycles due to "proxy" device links
> (needed for correctness of sync_state() device callback) will never fail
> device_link_add() due to cycles.
> 
> So, continuing to retry failing device links (by returning -EAGAIN) is
> no longer useful. At worst, it prevents platforms from setting
> fw_devlink=on (or better) because it prevents proper boot up. So, let's
> not do that anymore.
> 
> [1] - 
> https://lore.kernel.org/lkml/20191028220027.251605-1-saravanak@google.com/
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---

Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

Thanks!
Nicolas

On Thu, Apr 16, 2020 at 3:58 PM Saravana Kannan <saravanak@google.com> wrote:
>
> When of_link_to_phandle() was implemented initially, there was no way to
> tell if device_link_add() was failing because the supplier device hasn't
> been parsed yet, hasn't been added yet, the links were creating a cycle,
> etc. Some of these were transient errors that'd go away at a later
> point.
>
> However, with the current set of improved checks, if device_link_add()
> fails, it'll only be for permanent errors like cycles or out-of-memory
> errors.

What improved checks? The series from Nicolas?

Is there a dependency between this and Nicolas' series?

Should this go to stable?


>
> Also, with the addition of DL_FLAG_SYNC_STATE_ONLY flag [1] to device
> links, all the valid dependency cycles due to "proxy" device links
> (needed for correctness of sync_state() device callback) will never fail
> device_link_add() due to cycles.
>
> So, continuing to retry failing device links (by returning -EAGAIN) is
> no longer useful. At worst, it prevents platforms from setting
> fw_devlink=on (or better) because it prevents proper boot up. So, let's
> not do that anymore.
>
> [1] - https://lore.kernel.org/lkml/20191028220027.251605-1-saravanak@google.com/
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
>  drivers/of/property.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 252e4f600155..ee1bc267f975 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1074,7 +1074,7 @@ static int of_link_to_phandle(struct device *dev, struct device_node *sup_np,
>                 return -EAGAIN;
>         }
>         if (!device_link_add(dev, sup_dev, dl_flags))
> -               ret = -EAGAIN;
> +               ret = -EINVAL;
>         put_device(sup_dev);
>         return ret;
>  }
> --
> 2.26.1.301.g55bc3eb7cb9-goog
>

On Fri, Apr 17, 2020 at 11:16 AM Rob Herring <robh+dt@kernel.org> wrote:
>
> On Thu, Apr 16, 2020 at 3:58 PM Saravana Kannan <saravanak@google.com> wrote:
> >
> > When of_link_to_phandle() was implemented initially, there was no way to
> > tell if device_link_add() was failing because the supplier device hasn't
> > been parsed yet, hasn't been added yet, the links were creating a cycle,
> > etc. Some of these were transient errors that'd go away at a later
> > point.
> >
> > However, with the current set of improved checks, if device_link_add()
> > fails, it'll only be for permanent errors like cycles or out-of-memory
> > errors.
>
> What improved checks? The series from Nicolas?
>

Checking for OF_POPULATED and getting the device using get_dev_from_fwnode().
OF_POPULATED ensures the node has been parsed. get_dev_from_fwnode()
ensures the device has been added to driver core.

> Is there a dependency between this and Nicolas' series?

No.

> Should this go to stable?

Kind of a grey area. I mean, if of/fw_devlink is already letting a
platform boot all the way, this doesn't fix anything. I doubt anyone
in a stable kernel is turning on this feature if it affects device
probing. I'd say the same for Nicolas' series too. It allows more
platforms to work, but if a platform is fully working, it doesn't
improve anything.

Long story short, your call for stable.

-Saravana

On Thu, 16 Apr 2020 13:58:38 -0700, Saravana Kannan wrote:
> When of_link_to_phandle() was implemented initially, there was no way to
> tell if device_link_add() was failing because the supplier device hasn't
> been parsed yet, hasn't been added yet, the links were creating a cycle,
> etc. Some of these were transient errors that'd go away at a later
> point.
> 
> However, with the current set of improved checks, if device_link_add()
> fails, it'll only be for permanent errors like cycles or out-of-memory
> errors.
> 
> Also, with the addition of DL_FLAG_SYNC_STATE_ONLY flag [1] to device
> links, all the valid dependency cycles due to "proxy" device links
> (needed for correctness of sync_state() device callback) will never fail
> device_link_add() due to cycles.
> 
> So, continuing to retry failing device links (by returning -EAGAIN) is
> no longer useful. At worst, it prevents platforms from setting
> fw_devlink=on (or better) because it prevents proper boot up. So, let's
> not do that anymore.
> 
> [1] - https://lore.kernel.org/lkml/20191028220027.251605-1-saravanak@google.com/
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
>  drivers/of/property.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Applied, thanks.

Rob