linux-kernel - Re: [PATCH 1/6] driver-core: platform: Provide helpers for multi-driver modules

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Date:	Mon, 28 Sep 2015 09:37:37 +0300
From:	Jani Nikula <jani.nikula@...ux.intel.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	dri-devel@...ts.freedesktop.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] driver-core: platform: Provide helpers for multi-driver modules

On Fri, 25 Sep 2015, Thierry Reding <thierry.reding@...il.com> wrote:
> On Fri, Sep 25, 2015 at 01:27:28PM +0300, Jani Nikula wrote:
>> On Thu, 24 Sep 2015, Thierry Reding <thierry.reding@...il.com> wrote:
> [...]
>> > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> [...]
>> > +/**
>> > + * platform_register_drivers - register an array of platform drivers
>> > + * @drivers: an array of drivers to register
>> > + * @count: the number of drivers to register
>> > + *
>> > + * Registers platform drivers specified by an array. On failure to register a
>> > + * driver, all previously registered drivers will be unregistered. Callers of
>> > + * this API should use platform_unregister_drivers() to unregister drivers in
>> > + * the reverse order.
>> > + *
>> > + * Returns: 0 on success or a negative error code on failure.
>> > + */
>> > +int platform_register_drivers(struct platform_driver * const *drivers,
>> > +			      unsigned int count)
>> > +{
>> > +	unsigned int i;
>> > +	int err;
>> > +
>> > +	for (i = 0; i < count; i++) {
>> > +		pr_debug("registering platform driver %ps\n", drivers[i]);
>> > +
>> > +		err = platform_driver_register(drivers[i]);
>> > +		if (err < 0) {
>> > +			pr_err("failed to register platform driver %ps: %d\n",
>> > +			       drivers[i], err);
>> > +			goto error;
>> > +		}
>> > +	}
>> > +
>> > +	return 0;
>> > +
>> > +error:
>> > +	while (i--) {
>> > +		pr_debug("unregistering platform driver %ps\n", drivers[i]);
>> > +		platform_driver_unregister(drivers[i]);
>> > +	}
>> 
>> This will call platform_driver_unregister() on the driver that failed,
>> but not the first driver.
>> 
>> You should probably make i an int, and use while (--i >= 0).
>
> Actually it won't. I was especially careful and even tested this with
> one driver by instrumenting platform_driver_register() to return failure
> at various points in the sequence.
>
> This works fine.

You are right, of course. What was I thinking. My kingdom for an excuse!

BR,
Jani.




-- 
Jani Nikula, Intel Open Source Technology Center
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