Re: [PATCH v7 4/9] driver: core: allow modifying device_links flags

["Nuno Sá" <noname.nuno@gmail.com>]

On Thu, 2024-01-25 at 09:14 +0100, Nuno Sá wrote:
> 
> Hi Saravana,
> 
> Thanks for your feedback,
> 
> On Wed, 2024-01-24 at 19:21 -0800, Saravana Kannan wrote:
> > On Tue, Jan 23, 2024 at 7:14 AM Nuno Sa via B4 Relay
> > <devnull+nuno.sa.analog.com@kernel.org> wrote:
> > > 
> > > From: Nuno Sa <nuno.sa@analog.com>
> > > 
> > > If a device_link is previously created (eg: via
> > > fw_devlink_create_devlink()) before the supplier + consumer are both
> > > present and bound to their respective drivers, there's no way to set
> > > DL_FLAG_AUTOREMOVE_CONSUMER anymore while one can still set
> > > DL_FLAG_AUTOREMOVE_SUPPLIER. Hence, rework the flags checks to allow
> > > for DL_FLAG_AUTOREMOVE_CONSUMER in the same way
> > > DL_FLAG_AUTOREMOVE_SUPPLIER is done.
> > 
> > Curious, why do you want to set DL_FLAG_AUTOREMOVE_CONSUMER?
> > Especially if fw_devlink already created the link? You are effectively
> > trying to delete the link fw_devlink created if any of your devices
> > unbind.
> > 
> 
> Well, this is still useful in the modules case as the link will be relaxed
> after
> all devices are initialized and that will already clear AUTOPROBE_CONSUMER
> AFAIU. But, more importantly, if I'm not missing anything, in [1], fw_devlinks
> will be dropped after the consumer + supplier are bound which means I
> definitely
> want to create a link between my consumer and supplier. 
> 

Ok, so to add a bit more on this, there are two cases:

1) Both sup and con are modules and after boot up, the link is relaxed and thus
turned into a sync_state_only link. That means the link will be deleted anyways
and AUTOPROBE_CONSUMER is already cleared by the time we try to change the link.

2) The built-in case where the link is kept as created by fw_devlink and this
patch effectively clears AUTOPROBE_CONSUMER.

Given the above, not sure what's the best option. I can think of 4:

1) Drop this patch and leave things as they are. DL_FLAG_AUTOREMOVE_CONSUMER is
pretty much ignored in my call but it will turn the link in a MANAGED one and
clear SYNC_STATE_ONLY. I could very well just pass 0 in the flags as
DL_FLAG_AUTOREMOVE_CONSUMER is always ignored;

2) Rework this patch so we can still change an existing link to accept
DL_FLAG_AUTOREMOVE_CONSUMER (in the modules case for example).

However, instead of clearing AUTOPROBE_CONSUMER, I would add some checks so if
flags have one of DL_FLAG_AUTOREMOVE_SUPPLIER or DL_FLAG_AUTOREMOVE_CONSUMER and
AUTOPROBE_CONSUMER is already set, we ignore them. In fact, right now, I think
one could pass DL_FLAG_AUTOREMOVE_SUPPLIER and link->flags ends ups with
AUTOREMOVE_SUPPLIER | AUTOPROBE_CONSUMER which in theory is not allowed...

3) Keep it as-is... This one is likely a NACK as I'm getting the feeling that
clearing stuff that might have been created by fw_devlinks is probably a no-go.

Let me know your thoughts...

- Nuno Sá