linux-kernel - Re: [PATCH v3 3/3] arm: kernel: implement cpuidle

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Message-ID: <20150715144507.GZ7557@n2100.arm.linux.org.uk>
Date:	Wed, 15 Jul 2015 15:45:07 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Jisheng Zhang <jszhang@...vell.com>,
	Will Deacon <Will.Deacon@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"agross@...eaurora.org" <agross@...eaurora.org>,
	"davidb@...eaurora.org" <davidb@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] arm: kernel: implement cpuidle_ops with psci
 backend

On Wed, Jul 15, 2015 at 02:46:03PM +0100, Lorenzo Pieralisi wrote:
> On Tue, Jul 14, 2015 at 09:41:38PM +0100, Russell King - ARM Linux wrote:
> > Sorry, NAK, and end of discussion.  There is nothing more to be said
> > here.
> 
> I beg to differ. To solve the issue that you brought up with this series,
> we can create an arch function that allows to set CPUidle operations, which
> would remove the need for the OF construct you did not like, this mirrors
> what's done for PSCI smp operations (something similar to smp_set_ops),
> does that sound a reasonable approach to you ?

What's the point of that?

This is _all_ that arch/arm/kernel/psci_cpuidle.c will contain after this
series:

+#include <linux/cpuidle.h>
+#include <linux/psci.h>
+
+#include <asm/cpuidle.h>
+
+static struct cpuidle_ops psci_cpuidle_ops __initdata = {
+       .suspend = cpu_psci_cpu_suspend,
+       .init = cpu_psci_cpu_init_idle,
+};
+CPUIDLE_METHOD_OF_DECLARE(psci_cpuidle, "psci", &psci_cpuidle_ops);

There is _nothing_ ARM specific there.  All it's doing is providing an
entry in the DT linker-built table for that data structure, and that
data structure contains a pair of function pointers to code which _will_
be located in drivers/firmware/psci.c.

I'm saying _that_ is totally pointless, that data structure and
CPUIDLE_METHOD_OF_DECLARE() _should_ live with the code in
drivers/firmware/psci.c.

There's nothing in the above quoted code which points anything to any
32bit ARM specific stuff at all (so there's no need for a smp_set_ops()
type thing), it's all about giving DT a way to specify the CPU idle
operations which should be used, in this case, allowing DT to specify
that the _generic_ PSCI CPU idle operations are to be used.

> As for M.Rutland's series[1], and the patch that moves common PSCI code to
> drivers/firmware I reiterate my point, please review it[1] and provide us
> with feedback if any otherwise acknowledge the code move, which is the
> basis on top of which everything else can be developed, I do not understand
> why you are stopping [1] from getting into the kernel since it moves
> code from arch/arm to drivers/firmware to have it in a common and shared
> place between ARM and ARM64, what's the issue you have with that or put
> it differently why are you NAKing it ?

I'm NAKing everything related to moving the PSCI code around until
someone in the PSCI maintainer pool (that's not me - that's ARM Ltd)
clearly demonstrates that they know what they're talking about, and
has a plan behind this reorganisation.

Right now, I'm getting the impression that there is _no_ plan, or if
there is, it's an absurd plan which results in data structures which
should not be in arch/arm being left behind there.

-- 
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