linux-kernel - Re: [PATCH for review] [12/48] x86

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Date:	Fri, 20 Jul 2007 08:50:29 -0400
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
To:	"Andi Kleen" <ak@...e.de>
Cc:	tglx@...utronix.de, mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH for review] [12/48] x86_64: use the global PIT lock

On 7/20/07, Andi Kleen <ak@...e.de> wrote:
>
> > +static DEFINE_SPINLOCK(i8253_lock);
> > +
> > static __init int add_pcspkr(void)
> > {
> > struct platform_device *pd;
> > @@ -1501,9 +1503,14 @@ static __init int add_pcspkr(void)
> > if (!pd)
> > return -ENOMEM;
> >
> > +pd->dev.platform_data = &i8253_lock;
>
> That seems pretty ugly to pass spinlocks around in void * pointers.

That spinlock _is_ platform data. We could define

struct pcspkr_platform_data {
        spinlock_t *lock;
};

and pass around this as the rest of platform code does but then we'd
need a header file and it would add a level of indirection but if you
like this better I can change it. Otherwise spinlock is another data
structure and we pass them around all teh time.

> Also
> out of general memory bloat reasons i don't like allocating big data structures
> just for this.
>

I am not sure where you see new data structure allocation... If you
look at your box you should see that /sys/bus/platform/devices/pcspkr
device is already there. We already create it so that pcspkr driver
can bind to it.

> Wouldn't  it be better to just define i8253_lock weakly in the pcspkr code and let
> the architecture override it?

Yes, it probably is btetter.

>
> > Index: work/arch/x86_64/kernel/time.c
> > ===================================================================
> > --- work.orig/arch/x86_64/kernel/time.c
> > +++ work/arch/x86_64/kernel/time.c
> > @@ -23,6 +23,7 @@
> > #include <linux/module.h>
> > #include <linux/device.h>
> > #include <linux/sysdev.h>
> > +#include <linux/platform_device.h>
> > #include <linux/bcd.h>
> > #include <linux/notifier.h>
> > #include <linux/cpu.h>
> > @@ -185,7 +186,7 @@ void main_timer_handler(void)
> > set_rtc_mmss(xtime.tv_sec);
> > rtc_update = xtime.tv_sec + 660;
> > }
> > -
> > +
> > write_sequnlock(&xtime_lock);
> > }
>
> No random white space changes in patches, multiple occurrences ?!?
>

By bad, sorry.

-- 
Dmitry
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