linux-kernel - Re: [PATCH v9 4/7] nfc: pn533: Split pn533 init & nfc

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Date:   Wed, 16 Oct 2019 10:42:37 +0200
From:   Lars Poeschel <poeschel@...onage.de>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Jilayne Lovejoy <opensource@...ayne.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steve Winslow <swinslow@...il.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Johan Hovold <johan@...nel.org>,
        "open list:NFC SUBSYSTEM" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Claudiu Beznea <Claudiu.Beznea@...rochip.com>
Subject: Re: [PATCH v9 4/7] nfc: pn533: Split pn533 init & nfc_register

On Tue, Oct 15, 2019 at 09:16:42AM -0700, Jakub Kicinski wrote:
> On Tue, 15 Oct 2019 11:51:24 +0200, Lars Poeschel wrote:
> > > > -	priv->nfc_dev = nfc_allocate_device(&pn533_nfc_ops, protocols,
> > > > -					   priv->ops->tx_header_len +
> > > > -					   PN533_CMD_DATAEXCH_HEAD_LEN,
> > > > -					   priv->ops->tx_tail_len);
> > > > -	if (!priv->nfc_dev) {
> > > > -		rc = -ENOMEM;
> > > > -		goto destroy_wq;
> > > > -	}
> > > > -
> > > > -	nfc_set_parent_dev(priv->nfc_dev, parent);
> > > > -	nfc_set_drvdata(priv->nfc_dev, priv);
> > > > -
> > > > -	rc = nfc_register_device(priv->nfc_dev);
> > > > -	if (rc)
> > > > -		goto free_nfc_dev;  
> > > 
> > > Aren't you moving too much out of here? Looking at commit 32ecc75ded72
> > > ("NFC: pn533: change order operations in dev registation") it seems like
> > > IRQ handler may want to access the data structures, do this change not
> > > reintroduce the problem?  
> > 
> > Yes, you are right, there could be a problem if an irq gets served
> > before the driver is registered to the nfc subsystem.
> > Well, but the purpose of this patch is exactly that: Prevent use of nfc
> > subsystem before the chip is fully initialized.
> > To address this, I would not change the part above, but move the
> > request_threaded_irq to the very bottom in pn533_i2c_probe, after the
> > call to pn53x_register_nfc. So it is not possible to use nfc before the
> > chip is initialized and irqs don't get served before the driver is
> > registered to nfc subsystem.
> > Thank you for this!
> > I will include this in v10 of the patchset.
> 
> You can run nfc_allocate_device() etc. early, then allocate the IRQ,
> and then run nfc_register_device(), would that work? Is that what you
> have in mind?

Well, I think my proposed solution above would technically do it, but I
think I will do it like you proposed. I think for someone reading the
code it is far more easier to understand, what the idea behind it is, if
the irq is requested right between nfc_allocate_device and
nfc_register_device.
Thanks again!