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From: Marc Zyngier <marc.zyngier@arm.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Rich Felker <dalias@libc.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Sekhar Nori <nsekhar@ti.com>,
	Frank Rowand <frowand.list@gmail.com>,
	Linux-Arch <linux-arch@vger.kernel.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Kevin Hilman <khilman@kernel.org>,
	Bartosz Golaszewski <brgl@bgdev.pl>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Magnus Damm <magnus.damm@gmail.com>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	Jiri Slaby <jslaby@suse.com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	David Lechner <david@lechnology.com>,
	Arnd Bergmann <arnd@arndb.de>, Johan Hovold <johan@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Daniel
Subject: Re: [RESEND PATCH v3 3/3] sh: add the sh_ prefix to early platform symbols
Date: Tue, 23 Oct 2018 13:18:23 +0100	[thread overview]
Message-ID: <861s8gua9c.wl-marc.zyngier@arm.com> (raw)
In-Reply-To: <CAMuHMdWPPr56j3z4-eamtavt7cZ2jkKyE3W5_XiK1HNim8qXBg@mail.gmail.com>

Hi Geert,

On Tue, 23 Oct 2018 12:32:16 +0100,
Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> 
> Hi Marc,
> 
> On Tue, Oct 23, 2018 at 1:11 PM Marc Zyngier <marc.zyngier@arm.com> wrote:
> > On Mon, 27 Aug 2018 10:06:51 +0100,
> > Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> > As for the whole "early device" debate, my take is that we'd be much
> > better off making the device model available early, rather than trying
> > to architect something that is simply papering over the issue.
> 
> The device model itself can be made available earlier, but the big
> blocker is mainly the use of everything related to the scheduler
> (threads, msleep()), which depends on the "early" timer.

I agree this is an annoying dependency, as I've myself been down that
particular rabbit hole... ;-)

> I think it can be made to work if msleep() and all thread-related
> functions would return -EPROBE_DEFER, but that should be handled in
> every single driver, which may be already the case for
> thread-related functions, but not for e.g. msleep(), which currently
> returns void.

That would be massively invasive...

One way of solving this would be to make the device model available
early, but then preserve the ordering required by other subsystems
such as the scheduler: interrupts, timers and clocks have to be
available first, as they are basically at the root of all
dependencies.

This is a different kind of "early" though, as having the device model
early means all its functionalities are available early, and that
includes being able to allocate DMA buffers, which some interrupt
controllers require. The current proposal doesn't help with DMA, and
still leaves these devices in a state where drivers have to reinvent
their own square wheel.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.

WARNING: multiple messages have this Message-ID (diff)
From: marc.zyngier@arm.com (Marc Zyngier)
To: linux-arm-kernel@lists.infradead.org
Subject: [RESEND PATCH v3 3/3] sh: add the sh_ prefix to early platform symbols
Date: Tue, 23 Oct 2018 13:18:23 +0100	[thread overview]
Message-ID: <861s8gua9c.wl-marc.zyngier@arm.com> (raw)
In-Reply-To: <CAMuHMdWPPr56j3z4-eamtavt7cZ2jkKyE3W5_XiK1HNim8qXBg@mail.gmail.com>

Hi Geert,

On Tue, 23 Oct 2018 12:32:16 +0100,
Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> 
> Hi Marc,
> 
> On Tue, Oct 23, 2018 at 1:11 PM Marc Zyngier <marc.zyngier@arm.com> wrote:
> > On Mon, 27 Aug 2018 10:06:51 +0100,
> > Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> > As for the whole "early device" debate, my take is that we'd be much
> > better off making the device model available early, rather than trying
> > to architect something that is simply papering over the issue.
> 
> The device model itself can be made available earlier, but the big
> blocker is mainly the use of everything related to the scheduler
> (threads, msleep()), which depends on the "early" timer.

I agree this is an annoying dependency, as I've myself been down that
particular rabbit hole... ;-)

> I think it can be made to work if msleep() and all thread-related
> functions would return -EPROBE_DEFER, but that should be handled in
> every single driver, which may be already the case for
> thread-related functions, but not for e.g. msleep(), which currently
> returns void.

That would be massively invasive...

One way of solving this would be to make the device model available
early, but then preserve the ordering required by other subsystems
such as the scheduler: interrupts, timers and clocks have to be
available first, as they are basically at the root of all
dependencies.

This is a different kind of "early" though, as having the device model
early means all its functionalities are available early, and that
includes being able to allocate DMA buffers, which some interrupt
controllers require. The current proposal doesn't help with DMA, and
still leaves these devices in a state where drivers have to reinvent
their own square wheel.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.

  reply	other threads:[~2018-10-23 12:18 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-27  9:06 [RESEND PATCH v3 0/3] sh: make early_platform code SuperH-specific Bartosz Golaszewski
2018-08-27  9:06 ` Bartosz Golaszewski
2018-08-27  9:06 ` Bartosz Golaszewski
2018-08-27  9:06 ` [RESEND PATCH v3 1/3] clocksource: timer-ti-dm: remove the early platform driver registration Bartosz Golaszewski
2018-08-27  9:06   ` Bartosz Golaszewski
2018-08-27  9:06   ` Bartosz Golaszewski
2018-08-27  9:06 ` [RESEND PATCH v3 2/3] platform: move the early platform device support to arch/sh Bartosz Golaszewski
2018-08-27  9:06   ` Bartosz Golaszewski
2018-08-27  9:06   ` Bartosz Golaszewski
2018-08-27  9:06 ` [RESEND PATCH v3 3/3] sh: add the sh_ prefix to early platform symbols Bartosz Golaszewski
2018-08-27  9:06   ` Bartosz Golaszewski
2018-08-27  9:06   ` Bartosz Golaszewski
2018-10-23 11:10   ` Marc Zyngier
2018-10-23 11:10     ` Marc Zyngier
2018-10-23 11:10     ` Marc Zyngier
2018-10-23 11:32     ` Geert Uytterhoeven
2018-10-23 11:32       ` Geert Uytterhoeven
2018-10-23 11:32       ` Geert Uytterhoeven
2018-10-23 11:32       ` Geert Uytterhoeven
2018-10-23 12:18       ` Marc Zyngier [this message]
2018-10-23 12:18         ` Marc Zyngier
2018-09-20 13:00 ` [RESEND PATCH v3 0/3] sh: make early_platform code SuperH-specific Bartosz Golaszewski
2018-09-20 13:00   ` Bartosz Golaszewski
2018-09-20 13:00   ` Bartosz Golaszewski
2018-09-20 13:00   ` Bartosz Golaszewski
2018-09-20 16:09   ` Daniel Lezcano
2018-09-20 16:09     ` Daniel Lezcano
2018-09-20 16:09     ` Daniel Lezcano
2018-09-20 16:09     ` Daniel Lezcano
2018-09-20 16:19     ` Bartosz Golaszewski
2018-09-20 16:19       ` Bartosz Golaszewski
2018-09-20 16:19       ` Bartosz Golaszewski
2018-09-20 16:19       ` Bartosz Golaszewski
2018-09-20 16:48       ` Daniel Lezcano
2018-09-20 16:48         ` Daniel Lezcano
2018-09-20 16:48         ` Daniel Lezcano
2018-09-20 16:48         ` Daniel Lezcano
2018-10-09  7:58         ` Bartosz Golaszewski
2018-10-09  7:58           ` Bartosz Golaszewski
2018-10-09  7:58           ` Bartosz Golaszewski
2018-10-09  7:58           ` Bartosz Golaszewski
  -- strict thread matches above, loose matches on Subject: below --
2018-06-21  8:23 Bartosz Golaszewski
2018-06-21  8:23 ` [RESEND PATCH v3 3/3] sh: add the sh_ prefix to early platform symbols Bartosz Golaszewski
2018-06-21  8:23   ` Bartosz Golaszewski
2018-06-21  8:23   ` Bartosz Golaszewski

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