linux-kernel - Re: [PATCH 11/27] clocksource: sh_cmt: Add support for multiple channels per device

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Date:	Mon, 17 Feb 2014 11:07:06 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	SH-Linux <linux-sh@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 11/27] clocksource: sh_cmt: Add support for multiple
 channels per device

Hi Laurent,

On Mon, Feb 17, 2014 at 10:48 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> Hi Magnus,
>
> On Monday 17 February 2014 10:41:31 Magnus Damm wrote:
>> On Mon, Feb 17, 2014 at 3:18 AM, Laurent Pinchart wrote:
>> > On Saturday 15 February 2014 13:46:54 Thomas Gleixner wrote:
>> >> On Fri, 14 Feb 2014, Laurent Pinchart wrote:
>> >> > CMT hardware devices can support multiple channels, with global
>> >> > registers and per-channel registers. The sh_cmt driver currently models
>> >> > the hardware with one Linux device per channel. This model makes it
>> >> > difficult to handle global registers in a clean way.
>> >> >
>> >> > Add support for a new model that uses one Linux device per timer with
>> >> > multiple channels per device. This requires changes to platform data,
>> >> > add new channel configuration fields.
>> >> >
>> >> > Support for the legacy model is kept and will be removed after all
>> >> > platforms switch to the new model.
>> >> >
>> >> > Signed-off-by: Laurent Pinchart
>> >> > <laurent.pinchart+renesas@...asonboard.com>
>> >> > ---
>> >> >
>> >> >  drivers/clocksource/sh_cmt.c | 299 ++++++++++++++++++++++++++---------
>> >> >  include/linux/sh_timer.h     |   9 ++
>> >> >  2 files changed, 239 insertions(+), 69 deletions(-)
>> >> >
>> >> > diff --git a/drivers/clocksource/sh_cmt.c
>> >> > b/drivers/clocksource/sh_cmt.c
>> >> > index 5280231..8390f0f 100644
>> >> > --- a/drivers/clocksource/sh_cmt.c
>> >> > +++ b/drivers/clocksource/sh_cmt.c
>
> [snip]
>
>> >> > @@ -85,11 +94,15 @@ struct sh_cmt_info {
>> >> >
>> >> >  struct sh_cmt_channel {
>> >> >     struct sh_cmt_device *cmt;
>> >> > -   unsigned int index;
>> >> > -   void __iomem *base;
>> >> > +   unsigned int index;     /* Index in the documentation */
>> >> > +   unsigned int hwidx;     /* Real hardware index */
>> >> > +
>> >> > +   void __iomem *iostart;
>> >> > +   void __iomem *ioctrl;
>> >> >
>> >> >     struct irqaction irqaction;
>> >>
>> >> While you are at it, can you please get rid of that irqaction and use
>> >> request_irq() ?
>> >
>> > The driver claims it can't use request_irq() because the function is not
>> > available for early platform devices. If the situation has changed I'd
>> > gladly get rid of irqaction.
>>
>> With the risk of stating the obvious, this depends on how early the
>> early platform device stuff is being run. The actual location may not
>> be the same on SH and ARM for instance.
>>
>> On ARM we are doing all we can to initialize these devices as late as
>> ever possible in the MULTIPLAFORM (DT reference) case. Once we manage
>> to remove the legacy ARM case then there is one less user of early
>> platform timers.
>>
>> One perhaps reasonable way forward could be to use request_irq() in
>> case of DT and leave the legacy platform data case to rely on
>> irqaction.
>
> The whole point of switching from setup_irq() to request_irq() is to simplify
> the code. Adding request_irq() as an option would go in the opposite
> direction.

The point of switching to setup_irq() was not very clear to me. I
think it is fine to switch to using it over time, and I'm open to any
alternative ways forward. Usually moving in incremental steps means
more crap in the short term, but if someone could come up with a way
that involves little crap then I'm all for that! =)

Thanks,

/ magnus
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