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Re: [loongson-PATCH-v1 22/27] Hibernation Support in mips system

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: [loongson-PATCH-v1 22/27] Hibernation Support in mips system
From: yanh <yanh@lemote.com>
Date: Tue, 26 May 2009 09:43:08 +0800
Cc: wuzhangjin@gmail.com, linux-mips@linux-mips.org, ralf@linux-mips.org, philippe@cowpig.ca, r0bertz@gentoo.org, zhangfx@lemote.com, apatard@mandriva.com, loongson-dev@googlegroups.com, gnewsense-dev@nongnu.org, hofrat@hofr.at, liujl@lemote.com, erwan@thiscow.com
In-reply-to: <20090523.213045.39168996.anemo@mba.ocn.ne.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <817be0da759e19d781e98237cc70efeb33f10a40.1242855716.git.wuzhangjin@gmail.com> <20090522.220123.59650403.anemo@mba.ocn.ne.jp> <1243066003.8509.60.camel@localhost.localdomain> <20090523.213045.39168996.anemo@mba.ocn.ne.jp>
Reply-to: yanh@lemote.com
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在 2009-05-23六的 21:30 +0900,Atsushi Nemoto写道:
> On Sat, 23 May 2009 16:06:43 +0800, yanh <yanh@lemote.com> wrote:
> > > > +unsigned long
> > > > +       saved_ra,
> > > > +       saved_sp,
> ...
> > > > +       saved_v0,
> > > > +       saved_v1;
> > > 
> > > Instead of enumerating them, I would prefer something like "struct
> > > pt_regs saved_regs" or "unsigned long saved_regs[32]".
> > This implementation is referencing the x86 platform. 
> > Not all the 32 reigsters are needed to save. 
> > Maybe the whole registers needed to save can still be reduced.
> 
> I did not mean save/restore all registers.  I just mean using only one
> symbol (struct or array).  Though the struct or array contains some
> unused members, it saves many instructions in
> swsusp_arch_{suspend,resume}.
> 
> For saving N registers, (N * 2) instructions are required to save to
> individual variables, but (N + 2) instructions are required to save to
> array or struct.

Yes, the struct array method is more efficient, we will change to it.
> 
> > > > +void save_processor_state(void)
> > > > +{
> > > > +       saved_status = read_c0_status();
> > > > +}
> > > 
> > > No need to save/restore floating point registers?
> > the floating point registers are not used by kernel, for user part, they
> > are already saved while entering into kernel mode.
> 
> No, floating point registers are not saved on entering into kernel.
> They are saved on context switch.  
It's my mistake. But I think, if there is need to save floating point
registers, the kernel have already done for it. 
What's need to save should be for the resuming parts. Those registers which are 
used while 
in suspending path are needed to save.

create_image()

   in_suspend = 1;
    save_processor_state();
    error = swsusp_arch_suspend();
    if (error)
        printk(KERN_ERR "PM: Error %d creating hibernation image\n",
            error);
   
  when resuming this functions is executed for righ after the  
swsusp_arch_suspend().
  This is not a normal function return.
  So the registers need to save are those damaged by swsusp_arch_suspend and 
what it calls.
  
  because this is not a normal function call, the callee saved registers can 
not be restored, so we need to save
it explicitly. For caller saved temporary registers, they are already saved in 
create_image.  Are this right?
      
> 
> ---
> Atsushi Nemoto


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