linux-kernel - Re: [PATCH 1/2] device.h: pack struct dev_links

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Message-ID: <20190227133226.GQ4747@localhost>
Date:   Wed, 27 Feb 2019 14:32:26 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Johan Hovold <johan@...nel.org>, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 1/2] device.h: pack struct dev_links_info

On Wed, Feb 27, 2019 at 01:06:45PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Feb 27, 2019 at 11:59:51AM +0100, Johan Hovold wrote:

> Yeah, that is a good point, normally we use packed to keep padding from
> the middle of the structure from happening.
> 
> I just don't like that 4 bytes sitting there doing nothing :)

You could perhaps put them directly in struct device if the
dev_links_info struct is just used a separator there and this really
bothers you. :)

> But, in thinking about this, there is no real reason that I can see that
> this structure even is in struct device.  It should be able to be in the
> private "internal" structure.
> 
> The patch below moves it out of struct device entirely.  Overall there
> is no memory savings, but it could give us the chance to only create
> this structure if we really need it later on, as very few things use
> links at this point in time.
> 
> Rafael, there is one logic change below, the link structure is not
> initialized until device_add() happens, instead of device_initialize().
> Will that affect anything that you can think of?  Does anyone do
> anything with links before device_add() is called?

I think device_add() may be too late.

	The earliest point in time when device links can be added is
	after :c:func:`device_add()` has been called for the supplier
	and :c:func:`device_initialize()` has been called for the
	consumer.

Johan