Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756461Ab1FFR0I (ORCPT ); Mon, 6 Jun 2011 13:26:08 -0400 Received: from na3sys009aog111.obsmtp.com ([74.125.149.205]:54934 "EHLO na3sys009aog111.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292Ab1FFR0F (ORCPT ); Mon, 6 Jun 2011 13:26:05 -0400 Date: Mon, 6 Jun 2011 20:25:57 +0300 From: Felipe Balbi To: Alan Stern Cc: Felipe Balbi , "Rafael J. Wysocki" , Keshava Munegowda , USB list , linux-omap@vger.kernel.org, Kernel development list , gadiyar@ti.com, sameo@linux.intel.com, parthab@india.ti.com, tony@atomide.com, khilman@ti.com, b-cousson@ti.com, paul@pwsan.com Subject: Re: [PATCH 4/4] mfd: global Suspend and resume support of ehci and ohci Message-ID: <20110606172555.GL12242@legolas.emea.dhcp.ti.com> Reply-To: balbi@ti.com References: <20110605195413.GC18731@legolas.emea.dhcp.ti.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="lHuqAdgBYNjQz/wy" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9044 Lines: 280 --lHuqAdgBYNjQz/wy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Mon, Jun 06, 2011 at 12:06:44PM -0400, Alan Stern wrote: > > > > So, something like: > > > >=20 > > > > #define __pm_ops __section(.pm.ops) > > > >=20 > > > > static const struct dev_pm_ops my_driver_pm_ops __pm_ops =3D { > > > > .suspend =3D my_driver_suspend, > > > > .resume =3D my_driver_resume, > > > > [ blablabla ] > > > > }; > > > >=20 > > > > to simplify things, you could: > > > >=20 > > > > #define DEFINE_DEV_PM_OPS(_ops) \ > > > > const struct dev_pm_ops _ops __pm_ops > > > >=20 > > > > that would mean changes to all linker scripts, though and a utility= call > > > > that only does anything ifndef CONFIG_PM to free the .pm.ops sectio= n. > > >=20 > > > In my opinion this would make programming harder, not easier. It's > >=20 > > I tend to disagree with this statement, see below. > >=20 > > > very easy to understand "#ifdef" followed by "#endif"; people see them > >=20 > > very true... Still everybody has to put them in place. >=20 > True. But with your suggestion, people have to remember to use=20 > __pm_ops and DEFINE_DEV_PM_OPS. Ok, I see your point here. > > > all the time. The new tags you propose would force people to go > > > searching through tons of source files to see what they mean, and then > >=20 > > only those who want to see "how things work" would be forced to do that, > > other people would be allowed to "assume it's doing the right thing". >=20 > But what is the "right thing"? Suppose you want to have conditional=20 > support for dev_pm_ops whenever CONFIG_PM is enabled and you _also_=20 > want to have conditional support for runtime PM whenever=20 > CONFIG_PM_RUNTIME is enabled? we don't have this today either. Currently everybody does #ifdef CONFIG_PM, so either all the data is available, or none is and adding another #ifdef CONFIG_PM_RUNTIME for the runtime_* friends, would just look even uglier :-) > > > readers would still have to figure out when these tags should be used > > > or what advantage they might bring. > >=20 > > not really, if you add a macro which adds that correctly and during > > review we only accept drivers using that particular macro, things > > wouldn't go bad at all. > >=20 > > > It's a little like "typedef struct foo foo_t;" -- doing this forces > >=20 > > hey c'mon. Then you're saying that all __initdata, __devinitdata, > > __initconst and all of those are "typedef struct foo foo_t" ;-) >=20 > No. Unlike foo_t, they don't obscure important information and they do= =20 > provide a significant gain in simplicity. On the other hand, they also= =20 > provide a certain degree of confusion. Remember all the difficulty we=20 > had with intialization code sections in the gadget framework. this is fairly true, but only because the gadget framework isn't really a framework. It's just an agreement that all UDCs will export a particular function. It's a great infrastructure for the function drivers, but not for UDCs, so I think this isn't a great example :-) > > > people to remember one extra piece of information that serves no real > > > purpose except perhaps a minimal reduction in the amount of typing. = =20 > >=20 > > and a guarantee that the unused data will be freed when it's really not > > needed ;-) >=20 > You can obtain that same guarantee by using #ifdef ... #endif. Even=20 > better, you can guarantee that the unused data won't be present at all,= =20 > as opposed to loaded and then freed. I agree with you here, but I give you the same question as you gave me. How will you have conditional on CONFIG_RUNTIME_PM and CONFIG_PM ? you'd need two levels of ifdefs. > > > Since the limiting factor in kernel programming is human brainpower, > > > not source file length, this is a bad tradeoff. (Not to mention that > >=20 > > OTOH we are going through a big re-factor of the ARM port to reduce the > > amount of code. Not that these few characters would change much but my > > point is that amount of code also matters. So does uniformity, coding > > style, etc... > >=20 > > > it also obscures an important fact: A foo_t is an extended structure > > > rather than a single value.) > >=20 > > then it would make sense to have dev_pm_ops only defined when CONFIG_PM > > is set to force all drivers stick to a common way of handling this. > >=20 > > Besides, currently, everybody who wants to keep the ifdeferry, needs to > > define a macro for &my_dev_pm_ops or have two #ifdef..#endif blocks. > >=20 > > Either you do: > >=20 > > #ifdef CONFIG_PM > > static int my_driver_suspend(struct device *dev) > > { > > ... > >=20 > > return 0; > > } > > .... > >=20 > > static const struct dev_pm_ops my_driver_pm_ops =3D { > > .suspend =3D my_driver_suspend, > > ... > > }; > >=20 > > #define DEV_PM_OPS (&my_driver_pm_ops) > > #else > > #define DEV_PM_OPS NULL > > #endif > >=20 > > static struct platform_driver my_driver =3D { > > ... > > .driver =3D { > > .pm =3D DEV_PM_OPS > > }, > > }; > >=20 > > or you do: > >=20 > > #ifdef CONFIG_PM > > static int my_driver_suspend(struct device *dev) > > { > > ... > >=20 > > return 0; > > } > > .... > >=20 > > static const struct dev_pm_ops my_driver_pm_ops =3D { > > .suspend =3D my_driver_suspend, > > ... > > }; > >=20 > > #endif > >=20 > > static struct platform_driver my_driver =3D { > > ... > > .driver =3D { > > #ifdef CONFIG_PM > > .pm =3D &my_driver_pm_ops, > > #endif > > }, > > }; >=20 > Whereas your way people write: >=20 > static int __pm_ops my_driver_suspend(struct device *dev) > { > ... >=20 > return 0; > } > .... >=20 > static DEFINE_DEV_PM_OPS(my_driver_pm_ops) =3D { > .suspend =3D my_driver_suspend, > ... > }; >=20 > static struct platform_driver my_driver =3D { > ... > .driver =3D { > .pm =3D &my_driver_pm_ops, > }, > }; >=20 > It doesn't seem like a good idea to keep the invalid pointer to=20 > my_driver_pm_ops, even though it should never get used. true, I agree. > An approach that might work better would be for the PM core to define a= =20 > suitable macro: >=20 > #ifdef CONFIG_PM > #define DEV_PM_OPS_REF(my_pm_ops) &(my_pm_ops) > #else > #define DEV_PM_OPS_REF(my_pm_ops) NULL > #endif >=20 > Then people could write >=20 > static struct platform_driver my_driver =3D { > ... > .driver =3D { > .pm =3D DEV_PM_OPS_REF(my_driver_pm_ops), > }, > }; >=20 > without worrying about whether or not my_driver_pm_ops was defined. =20 > And only one #ifdef block would be needed. that'd be nice. Something similar to __exit_p() and __devexit_p() > > So, while this is a small thing which is easy to understand, it's still > > yet another thing that all drivers have to remember to add. And when > > everybody needs to remember that, I'd rather have it done > > "automatically" by other means. > >=20 > > I mean, we already free .init.* sections after __init anyway, so what's > > the problem in freeing another section ? I don't see it as obfuscation > > at all. I see it as if the kernel is smart enough to free all unused > > data by itself, without myself having to add ifdefs or freeing it by my > > own. > >=20 > > On top of all that, today, we have driver with both ways of ifdefs plus > > drivers with no ifdeferry at all, leaving dev_pm_ops floating around for > > nothing. > >=20 > > IMHO, if things aren't uniform, we will have small problems, such as > > this, proliferate because new drivers are based on other drivers, > > generally. >=20 > I have to agree that uniformity is to be desired. And it's probably=20 > already way too late, because we can't prevent new drivers from being=20 I wouldn't call it late. Such small convertions can be done by simple scripts, but when patches switching drivers over are rejected [1] then we loose the opportunity to give good example to newcomers. > based on the existing drivers -- even if all the existing drivers get=20 > changed over (which seems unlikely). Well, it might work out if pm core makes dev_pm_ops only available on CONFIG_PM builds. 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