RE: [PATCH v2 09/10] hw/intc: Remove redundant statement in exynos4210_combiner_read()

[Chenqun (kuhn)]

> Subject: Re: [PATCH v2 09/10] hw/intc: Remove redundant statement in
> exynos4210_combiner_read()
> 
> On Tue, 25 Aug 2020 at 12:26, Chen Qun <kuhn.chenqun@huawei.com> wrote:
> >
> > Clang static code analyzer show warning:
> > hw/intc/exynos4210_combiner.c:231:9: warning: Value stored to 'val' is never
> read
> >         val = s->reg_set[offset >> 2];
> >
> > The default value of 'val' is '0', so we can break the 'default' branch and 
> > return
> 'val'.
> >
> > Reported-by: Euler Robot <euler.robot@huawei.com>
> > Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
> > ---
> > Cc: Igor Mitsyanko <i.mitsyanko@gmail.com>
> > Cc: Peter Maydell <peter.maydell@linaro.org>
> > ---
> >  hw/intc/exynos4210_combiner.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/hw/intc/exynos4210_combiner.c
> > b/hw/intc/exynos4210_combiner.c index b8561e4180..e2e745bbaa 100644
> > --- a/hw/intc/exynos4210_combiner.c
> > +++ b/hw/intc/exynos4210_combiner.c
> > @@ -228,8 +228,7 @@ exynos4210_combiner_read(void *opaque, hwaddr
> offset, unsigned size)
> >              hw_error("exynos4210.combiner: overflow of reg_set by 0x"
> >                      TARGET_FMT_plx "offset\n", offset);
> >          }
> > -        val = s->reg_set[offset >> 2];
> > -        return 0;
> > +        break;
> >      }
> >      return val;
> >  }
> 
> The code as it stands is definitely wrong, but I'm not sure this is the 
> correct fix.
> Surely the intention must have been to return the actual register value from
> the reg_set[] array, not to return 0 ?
> 
> I suspect the correct fix here is simply to delete the "return 0" line and 
> leave
> the assignment to val as it is.

Hi Peter,
  I think you're right.

> Ideally you should check the h/w datasheet to confirm.
 I checked the Exynos 4210 datasheet and found that 'Interrupt Combiner 
Operation' had only five types of registers.

Register             Description                                              
Type
----------------------------------------------------------------------------------------------------------------------------------------
IESR(0/1/2/3)   Interrupt Enable Set Register for Group (0~3/ 4 ~7/ 8~ 11/ 12~ 
15)         RW
IECR(0/1/2/3)   Interrupt Enable Clear Register for Group (0~3/ 4 ~7/ 8~ 11/ 
12~ 15)       RW
ISTR(0/1/2/3)   Interrupt Status Register for Group (0~3/ 4 ~7/ 8~ 11/ 12~ 15)  
           R
IMSR(0/1/2/3)  Interrupt Masked Status Register for Group(0~3/ 4 ~7/ 8~ 11/ 12~ 
15)       R
CIPSR0        Combined Interrupt Pending Status0                                
  R

The exynos4210_combiner_write() function has write operations for IESR and IECR.
The CIPSR, ISTR, and IMSR read operations are specified in the 
exynos4210_combiner_read() function.

So, This 'default' branch in exynos4210_combiner_read() function read operation 
is only for IESR and IECR.

And, in the exynos4210_combiner_write function, the default assignment 
statement for IESR and IECR is " s->reg_set[offset >> 2] = val;".
Therefore, if we read the two register(IESR and IECR) values, we can directly 
use this assignment statement "val = s->reg_set[offset >> 2];".

Please confirm that if there is no problem, I will modify it in later version.

Thanks,
Chen Qun