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

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On Fri, 2024-01-26 at 09:04 +0100, Nuno Sá wrote:
> On Thu, 2024-01-25 at 17:57 +0100, Rafael J. Wysocki wrote:
> > On Thu, Jan 25, 2024 at 4:31 PM Nuno Sá <noname.nuno@xxxxxxxxx> wrote:
> > > 
> > > 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@xxxxxxxxxx> wrote:
> > > > > > 
> > > > > > From: Nuno Sa <nuno.sa@xxxxxxxxxx>
> > > > > > 
> > > > > > 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...
> > 
> > No, because DL_FLAG_AUTOREMOVE_SUPPLIER is only added to the link
> > flags if DL_FLAG_AUTOREMOVE_CONSUMER is already set in there and the
> > former replaces the latter.
> > 
> 
> Oh yes, I missed that extra if() against the DL_FLAG_AUTOREMOVE_CONSUMER
> flag...
> 
> > Now, DL_FLAG_AUTOREMOVE_CONSUMER cannot be set in the link flags if
> > AUTOPROBE_CONSUMER is set in there.
> > 
> > > 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...
> > 
> > If the original creator of the link didn't indicate either
> > DL_FLAG_AUTOREMOVE_CONSUMER, or DL_FLAG_AUTOREMOVE_SUPPLIER, they are
> > expected to need the link to stay around until it is explicitly
> > deleted.
> > 
> > Therefore adding any of these flags for an existing link where they
> > both are unset would be a mistake, because it would effectively cause
> > the link to live shorter than expected by the original creator and
> > that might lead to correctness issues.
> > 
> > Thanks!
> 
> Thanks Rafael, your last two paragraphs make it really clear what's the
> reasoning and why this patch is wrong.
> 
> Jonathan, if nothing else comes that I need a re-spin, can you drop this patch
> when applying?
> 
> I think we can keep the DL_FLAG_AUTOREMOVE_CONSUMER in the device_link_add()
> call as it will be ignored if fw_devlinks already created the link but might
> be
> important if the kernel command line fw_devlink is set to 'off'.
> 
> Or maybe, as Saravan mentioned in his reply we can just pass DL_FLAG_MANAGED
> as

Forget about this as I just realized DL_FLAG_MANAGED is not a proper flag we can
pass...

- Nuno Sá






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