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

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Date:   Thu, 24 Sep 2020 09:21:20 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Finn Thain <fthain@...egraphics.com.au>
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

Hi Finn,

On Thu, Sep 24, 2020 at 3:07 AM Finn Thain <fthain@...egraphics.com.au> wrote:
> On Wed, 16 Sep 2020, Finn Thain wrote:
> > 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.
> >
>
> Sorry, I meant to say, "I could have changed ide_host_add() into
> ide_host_alloc() followed by ide_host_register() ..."
>
> > 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"?
>
> I still think that "if it ain't broke, don't fix it" is actually the
> "safe" option for macide.c. But I'm happy to make additional changes, test
> them and send v5 if that's preferred.

I'm fine with keeping this as-is, as it doesn't really matter for this
particular
driver.

> Looking further at the drivers using ide_host_register(), I see that
> falconide.c is missing a set_drvdata() call, while tx4939ide.c calls
> set_drvdata() after ide_host_register(). The latter example is not a bug.
>
> The pattern I used, that is, calling set_drvdata() after ide_host_add(),
> is actually more popular among IDE drivers than the pattern you suggested,
> that is, set_drvdata() followed by ide_host_register(). Either way, I
> don't see any bugs besides the one in falconide.c.
>
> Regarding falconide.c, my inclination is to send a fix following the more
> common pattern (among IDE drivers), as below. I guess that may prompt the
> subsystem maintainers to make known their views on the style question.

Please do so. Thanks!


Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds