linux-kernel - Re: [RESEND PATCH] driver core: Clear FWNODE_FLAG_LINKS_ADDED in device_links

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Date:   Wed, 27 Sep 2023 10:08:47 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zhenhua Huang <quic_zhenhuah@...cinc.com>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        quic_pkondeti@...cinc.com, quic_tingweiz@...cinc.com,
        saravanak@...gle.com
Subject: Re: [RESEND PATCH] driver core: Clear FWNODE_FLAG_LINKS_ADDED in
 device_links_purge()

On Wed, Sep 27, 2023 at 02:34:43PM +0800, Zhenhua Huang wrote:
> 
> 
> On 2023/9/27 13:57, Greg KH wrote:
> > On Wed, Sep 27, 2023 at 10:30:10AM +0800, Zhenhua Huang wrote:
> > > Flag FWNODE_FLAG_LINKS_ADDED stops fwnode links creation. Current kernel
> > > only adds it once after fwnode links creation in fw_devlink_parse_fwnode().
> > > After that even device links being purged, the flag will not be cleared.
> > > 
> > > Fwnode links are converted to device links and will not be added back
> > > forever in normal case. Essentially if a device is registered and
> > > unregisted (also deleted) before it is probed (due to missing fwlink
> > > dependencies, abort in device_links_check_suppliers), the fwlink is not
> > > setup next when device is newly created again. This means the probe gets
> > > called without meeting all dependencies.
> > > 
> > > It usuallly happens in the case of a glue driver. Of_platform_populate()
> > > allows us to populate subnodes. We may do it in ancestor node probing
> > > function, then check subnode's probing status because there may be chances
> > > that suppliers of subnode are not ready. We may further need to do
> > > of_platform_depopulate(which purges device links) and in some time
> > > of_platform_populate() again. Such case we miss fwnode links(so that device
> > > links) during second time of populating subnodes.
> > > 
> > > Fix it by Clearing FWNODE_FLAG_LINKS_ADDED flag in purging device link
> > > func, indicates both fwnode links and device links are absent.
> > > 
> > > Signed-off-by: Zhenhua Huang <quic_zhenhuah@...cinc.com>
> > > ---
> > >   drivers/base/core.c | 4 ++++
> > >   1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > index b7d7f41..2a1975d 100644
> > > --- a/drivers/base/core.c
> > > +++ b/drivers/base/core.c
> > > @@ -1630,6 +1630,10 @@ static void device_links_purge(struct device *dev)
> > >   		__device_link_del(&link->kref);
> > >   	}
> > > +	/* Clear flags in fwnode. Give a chance to create fwnode link again */
> > > +	if (dev->fwnode)
> > > +		dev->fwnode->flags &= ~FWNODE_FLAG_LINKS_ADDED;
> > > +
> > >   	device_links_write_unlock();
> > >   }
> > > -- 
> > > 2.7.4
> > > 
> > 
> > Why is this a RESEND?  What was wrong with the first version?
> 
> As per request of codes author, I CCed saravanak this time :)
> Nothing else changed.

Please state that below the --- line, otherwise we have no idea why this
was needed, we can't read minds :)

thanks,

greg k-h