linux-kernel - Re: 8250.nr_uarts broken in 3.7

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Message-ID: <20130309170241.GR13719@hansolo.jdub.homelinux.org>
Date:	Sat, 9 Mar 2013 12:02:42 -0500
From:	Josh Boyer <jwboyer@...hat.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: 8250.nr_uarts broken in 3.7

On Sat, Mar 09, 2013 at 03:14:18PM +0100, Jiri Slaby wrote:
> On 03/09/2013 02:30 PM, Josh Boyer wrote:
> > From: Josh Boyer <jwboyer@...hat.com>
> > Date: Fri, 8 Mar 2013 21:13:52 -0500
> > Subject: [PATCH] serial: 8250: Keep 8250.<xxxx> module options functional
> >  after driver rename
> > 
> > With commit 835d844d1 (8250_pnp: do pnp probe before legacy probe), the
> > 8250 driver was renamed to 8250_core.  This means any existing usage of
> > the 8259.<xxxx> module parameters or as a kernel command line switch is
> > now broken, as the 8250_core driver doesn't parse options belonging to
> > something called "8250".
> > 
> > To solve this, we redefine the module options in a dummy function using
> > a redefined MODULE_PARAM_PREFX when built into the kernel.  In the case
> > where we're building as a module, we provide an alias to the old 8250
> > name.  The dummy function prevents compiler errors due to global variable
> > redefinitions that happen as part of the module_param_ macro expansions.
> > 
> > Signed-off-by: Josh Boyer <jwboyer@...hat.com>
> > ---
> >  drivers/tty/serial/8250/8250.c | 31 +++++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> > 
> > diff --git a/drivers/tty/serial/8250/8250.c b/drivers/tty/serial/8250/8250.c
> > index 0efc815..446beb7 100644
> > --- a/drivers/tty/serial/8250/8250.c
> > +++ b/drivers/tty/serial/8250/8250.c
> > @@ -3396,3 +3396,34 @@ module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444);
> >  MODULE_PARM_DESC(probe_rsa, "Probe I/O ports for RSA");
> >  #endif
> >  MODULE_ALIAS_CHARDEV_MAJOR(TTY_MAJOR);
> > +
> > +#ifndef MODULE
> > +/* This module was renamed to 8250_core in 3.7.  Keep the old "8250" name
> > + * working as well for the module options so we don't break people.  We
> > + * need to keep the names identical and the convenient macros will happily
> > + * refuse to let us do that by failing the build with redefinition errors
> > + * of global variables.  So we stick them inside a dummy function to avoid
> > + * those conflicts.  The options still get parsed, and the redefined
> > + * MODULE_PARAM_PREFIX lets us keep the "8250." syntax alive.  We redefine
> > + * __param_check to a throw away value to avoid type conflicts from the
> > + * expansion that would happen otherwise.
> > + *
> > + * This is hacky.  I'm sorry.
> > + */
> > +static void __used s8250_options(void)
> > +{
> > +#undef MODULE_PARAM_PREFIX
> > +#define MODULE_PARAM_PREFIX "8250."
> > +
> > +	module_param_cb(share_irqs, &param_ops_uint, &share_irqs, 0644);
> > +	module_param_cb(nr_uarts, &param_ops_uint, &nr_uarts, 0644);
> > +	module_param_cb(skip_txen_test, &param_ops_uint, &skip_txen_test, 0644);
> > +#ifdef CONFIG_SERIAL_8250_RSA
> > +#undef __param_check
> > +#define __param_check(name, p, type) int __attribute((unused)) tmp
> > +	module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444);
> 
> Aiee, we havo no _cb for arrays. But we can do just:
> __module_param_call(MODULE_PARAM_PREFIX, probe_rsa,
>        &param_array_ops, .arr = &__param_arr_probe_rsa,
>        0444, -1);

Right.  I can change that.  I just went for the simpler fix.

> > +#endif
> > +}
> > +#else
> > +MODULE_ALIAS("8250");
> 
> This is so disgusting that I will do the following:
> * ack your patch after you change the above (if that works)
> * rename 8250.c to 8250_core.c
> * change 8250_core.ko back to 8250.ko (ie. bring back the old module name)
> * thus switch MODULE_PARAM_PREFIX above to "8250_core."
> * deprecate all the newly added 8250_core.* params somehow and schedule
> for removal. IMO this warrants a kernel config option like
> CONFIG_8250_DEPRECATED_MODULE_PARAMS.
> 
> We have a lesson learned.

Heh, ok.  That all sounds fine.  I'll try to make the small revision
tonight and test it.

josh
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