linux-kernel - Re: [PATCH v2] ide/macide: Convert Mac IDE driver to platform driver

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Date:   Wed, 16 Sep 2020 08:56:58 +1000 (AEST)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     "David S. Miller" <davem@...emloft.net>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Joshua Thompson <funaho@...ai.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-ide@...r.kernel.org
Subject: Re: [PATCH v2] ide/macide: Convert Mac IDE driver to platform
 driver

On Tue, 15 Sep 2020, Geert Uytterhoeven wrote:

> > > > --- a/drivers/ide/macide.c
> > > > +++ b/drivers/ide/macide.c
> > >
> > > > @@ -109,42 +110,61 @@ static const char *mac_ide_name[] =
> > > >   * Probe for a Macintosh IDE interface
> > > >   */
> > > >
> > > > -static int __init macide_init(void)
> > > > +static int mac_ide_probe(struct platform_device *pdev)
> > > >  {
> > >
> > > >         printk(KERN_INFO "ide: Macintosh %s IDE controller\n",
> > > >                          mac_ide_name[macintosh_config->ide_type - 1]);
> > > >
> > > > -       macide_setup_ports(&hw, base, irq);
> > > > +       macide_setup_ports(&hw, mem->start, irq->start);
> > > >
> > > > -       return ide_host_add(&d, hws, 1, NULL);
> > > > +       rc = ide_host_add(&d, hws, 1, &host);
> > > > +       if (rc)
> > > > +               return rc;
> > > > +
> > > > +       platform_set_drvdata(pdev, host);
> > >
> > > Move one up, to play it safe?
> > >
> >
> > You mean, before calling ide_host_add? The 'host' pointer is uninitialized
> > prior to that call.
> 
> Oh right, so the IDE subsystem doesn't let you use the drvdata inside 
> your driver (besides in remove()) in a safe way :-(
> 

The IDE subsystem does allow other patterns here. I could have changed 
ide_host_alloc() into ide_host_register() followed by ide_host_add() but I 
could not see any benefit from that change.

A quick search for "platform_device" shows that the driver does not use 
any uninitialized driver_data pointer (because ide_ifr is a global). In 
your message of September 9th you readily reached the same conclusion when 
you reviewed v1.

If mac_ide_probe() followed the usual pattern it might make review easier 
(as reviewers may not wish to consider the entire driver) but does that 
really make the code more "safe"?