linux-kernel - Re: [Ksummit-2013-discuss] [ATTEND] [ARM ATTEND] kernel data bloat and how to avoid it

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Message-ID: <20130802124130.GI7656@atomide.com>
Date:	Fri, 2 Aug 2013 05:41:31 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Greg KH <greg@...ah.com>
Cc:	ksummit-2013-discuss@...ts.linuxfoundation.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [Ksummit-2013-discuss] [ATTEND] [ARM ATTEND] kernel data bloat
 and how to avoid it

* Tony Lindgren <tony@...mide.com> [130802 01:00]:
> * Greg KH <greg@...ah.com> [130731 05:39]:
> > On Wed, Jul 31, 2013 at 12:38:03AM -0700, Tony Lindgren wrote:
> > > Hi all,
> > > 
> > > Probably the biggest kernel data bloat issue is in the ARM land, but
> > > it also seems that it's becoming a Linux generic issue too, so I
> > > guess it could be discussed in either context.
> > 
> > Why is it specific to ARM?  What is so unique to ARM that causes it to
> > "bloat"?
> 
> I think it has so far showed up on ARM because of no discoverable busses,
> but chances are it will be more of a generic problem.
> 
> > And what exactly do you mean by "bloat"?
> 
> Stuffing data to kernel that should not be in the kernel at all. Or
> if the data is needed by kernel, there should be only one set of the
> data defined rather than multiple copies of the data built into the
> kernel for each SoC or driver variant.
> 
> > > Basically the data bloat issue is there for the arch code and drivers
> > > and may not show up initially until things have headed the wrong way for
> > > too long.
> > 
> > What do you mean by this?  You seem to be very vague here.
> 
> People are unnecessarily defining registers in kernel for similar devices
> over and over again for each new SoC at the arch level and now more and
> more at the driver level.
> 
> One example of that are device tree based drivers that don't describe
> the actual hardware, but instead have a binding that points to an index
> of defined registers in the driver.
> 
> One way to avoid these kind of bloat issues is to allow drivers to load
> data at multiple points: Only abtolutely minimal set of data should be
> static, some should only come from the bootloader as a device tree or
> ACPI tables, and some is best to be loaded after booting from /lib/firmware.

Oh and thinking about it a bit more, this issue is mostly with the
device drivers implementing frameworks, not the device drivers
using the frameworks. Things like clocks, regulators, muxes etc where
an almost similar instance is repeated tens or hundreds of times for
each SoC.

Regards,

Tony
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