linux-kernel - Re: [PATCH 1/2] serial: samsung: Move uart_register

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Message-ID: <20140121092531.350ab714@alan.etchedpixels.co.uk>
Date:	Tue, 21 Jan 2014 09:25:31 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Tushar Behera <tushar.behera@...aro.org>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, jslaby@...e.cz,
	ben.dooks@...ethink.co.uk, broonie@...nel.org
Subject: Re: [PATCH 1/2] serial: samsung: Move uart_register_driver call to
 device probe

> > So, let's go back to your original worry, what are you concerned about?
> > A device being removed while probe() is called?
> 
> My concern is that we're turning something which should be simple into
> something unnecessarily complex.  By that, I mean something along the
> lines of:

Or in fact more complex in other cases because your remove may well be
refcounted so the stuff may not be going away in the foo_remove() path.

> 
> static DEFINE_MUTEX(foo_mutex);
> static unsigned foo_devices;
> 
> static int foo_probe(struct platform_device *pdev)
> {
> 	int ret;
> 
> 	mutex_lock(&foo_mutex);
> 	if (foo_devices++ == 0)
> 		uart_register_driver(&driver);
> 
> 	ret = foo_really_probe_device(pdev);

We have atomic_inc_and_test and atomic_dec_and_test so it's
fractionally less ugly.

> in every single serial driver we have...  Wouldn't it just be better to
> fix the major/minor number problem rather than have to add all that code
> repetitively to all those drivers?

Quite.

Although for some drivers I suspect what is actually missing when built
in is

module_init() {
	if (not_the_right_platform())
		return -ENOGOOD;
}

 
Going dynamic is the right fix though. Changing how the driver
registration work is a different (and quite independent) problem.

Alan
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