drm/mgag200: don't use uninitialized variables in mga_g200se_set_plls()

drm/mgag200: don't use uninitialized variables in mga_g200se_set_plls()

[Jan Beulich]

I can only guess that instead of testm/testn (which are either
uninitialized or have pre-determined values at the end of the preceding
loops) n and m were meant to be used by commit e829d7ef9f
("drm/mgag200: Add support for a new rev of G200e"). In any event the
compiler is right in warning that testm/testn are possibly uninitalized
at this point, i.e. some change is needed no matter what.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Mathieu Larouche <mathieu.larouche@matrox.com>
---
 drivers/gpu/drm/mgag200/mgag200_mode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 4.3-rc6/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ 4.3-rc6-mgag200-uninit/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -194,7 +194,7 @@ static int mga_g200se_set_plls(struct mg
 			}
 		}
 
-		fvv = pllreffreq * testn / testm;
+		fvv = pllreffreq * n / m;
 		fvv = (fvv - 800000) / 50000;
 
 		if (fvv > 15)



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Re: drm/mgag200: don't use uninitialized variables in mga_g200se_set_plls()

[Mathieu Larouche]

On 19/10/2015 6:29 AM, Jan Beulich wrote:
> I can only guess that instead of testm/testn (which are either
> uninitialized or have pre-determined values at the end of the preceding
> loops) n and m were meant to be used by commit e829d7ef9f
> ("drm/mgag200: Add support for a new rev of G200e"). In any event the
> compiler is right in warning that testm/testn are possibly uninitalized
> at this point, i.e. some change is needed no matter what.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Cc: Mathieu Larouche <mathieu.larouche@matrox.com>
> ---
>   drivers/gpu/drm/mgag200/mgag200_mode.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- 4.3-rc6/drivers/gpu/drm/mgag200/mgag200_mode.c
> +++ 4.3-rc6-mgag200-uninit/drivers/gpu/drm/mgag200/mgag200_mode.c
> @@ -194,7 +194,7 @@ static int mga_g200se_set_plls(struct mg
>   			}
>   		}
>   
> -		fvv = pllreffreq * testn / testm;
> +		fvv = pllreffreq * n / m;
>   		fvv = (fvv - 800000) / 50000;
>   
>   		if (fvv > 15)
>
>
>
>
If you are using n/m instead of testn/testm, you need to
add 1 to the variables to keep consistency. However, you
have the same issue where m/n could be used without being
initialized. So, I propose to keep testm, testn & testp
and initialized them with the default value.

Signed-off-by: Mathieu Larouche <mathieu.larouche@matrox.com>
---
  drivers/gpu/drm/mgag200/mgag200_mode.c | 6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
index c99d3fe..055799c 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -123,6 +123,9 @@ static int mga_g200se_set_plls(struct mga_device *mdev, long clock)
  		vcomax = 320000;
  		vcomin = 160000;
  		pllreffreq = 25000;
+		testm = 1;
+		testn = 17;
+		testp = 8;
  
  		delta = 0xffffffff;
  		permitteddelta = clock * 5 / 1000;
@@ -157,6 +160,9 @@ static int mga_g200se_set_plls(struct mga_device *mdev, long clock)
  		vcomax        = 1600000;
  		vcomin        = 800000;
  		pllreffreq    = 25000;
+		testm         = 1;
+		testn         = 50;
+		testp         = 16;
  
  		if (clock < 25000)
  			clock = 25000;

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Re: drm/mgag200: don't use uninitialized variables in mga_g200se_set_plls()

[Jan Beulich]

>>> On 20.10.15 at 16:47, <mathieu.larouche@matrox.com> wrote:
> On 19/10/2015 6:29 AM, Jan Beulich wrote:
>> --- 4.3-rc6/drivers/gpu/drm/mgag200/mgag200_mode.c
>> +++ 4.3-rc6-mgag200-uninit/drivers/gpu/drm/mgag200/mgag200_mode.c
>> @@ -194,7 +194,7 @@ static int mga_g200se_set_plls(struct mg
>>   			}
>>   		}
>>   
>> -		fvv = pllreffreq * testn / testm;
>> +		fvv = pllreffreq * n / m;
>>   		fvv = (fvv - 800000) / 50000;
>>   
>>   		if (fvv > 15)
>>
> If you are using n/m instead of testn/testm, you need to
> add 1 to the variables to keep consistency. However, you
> have the same issue where m/n could be used without being
> initialized. So, I propose to keep testm, testn & testp
> and initialized them with the default value.

That makes them initialized, but since testn and testm are used
as loop variables I don't see how initializing them to default
values helps overcome the other half of the problem described
(them having a constant, pre-determined value at the end of
the loops: testn=257, testm=33). As to testp - it is always
initialized anyway (so long as P_ARRAY_SIZE is not zero). And
in the if() branch initialization isn't needed either, since the
variables aren't being used after the loops.

Jan

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Re: drm/mgag200: don't use uninitialized variables in mga_g200se_set_plls()

[Mathieu Larouche]

On 20/10/2015 11:00 AM, Jan Beulich wrote:
>>>> On 20.10.15 at 16:47, <mathieu.larouche@matrox.com> wrote:
>> On 19/10/2015 6:29 AM, Jan Beulich wrote:
>>> --- 4.3-rc6/drivers/gpu/drm/mgag200/mgag200_mode.c
>>> +++ 4.3-rc6-mgag200-uninit/drivers/gpu/drm/mgag200/mgag200_mode.c
>>> @@ -194,7 +194,7 @@ static int mga_g200se_set_plls(struct mg
>>>    			}
>>>    		}
>>>    
>>> -		fvv = pllreffreq * testn / testm;
>>> +		fvv = pllreffreq * n / m;
>>>    		fvv = (fvv - 800000) / 50000;
>>>    
>>>    		if (fvv > 15)
>>>
>> If you are using n/m instead of testn/testm, you need to
>> add 1 to the variables to keep consistency. However, you
>> have the same issue where m/n could be used without being
>> initialized. So, I propose to keep testm, testn & testp
>> and initialized them with the default value.
> That makes them initialized, but since testn and testm are used
> as loop variables I don't see how initializing them to default
> values helps overcome the other half of the problem described
> (them having a constant, pre-determined value at the end of
> the loops: testn=257, testm=33). As to testp - it is always
> initialized anyway (so long as P_ARRAY_SIZE is not zero). And
> in the if() branch initialization isn't needed either, since the
> variables aren't being used after the loops.
>
> Jan
>
>
Sorry, I missed that part in your initial comment and you are right,
there's an issue there. So, your proposed patch totally make sense,
you only need to add 1 to m/n.

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[PATCH v2] drm/mgag200: don't use uninitialized variables in mga_g200se_set_plls()

[Jan Beulich]

I can only guess that instead of testm/testn (which are either
uninitialized or have pre-determined values at the end of the preceding
loops) n and m were meant to be used by commit e829d7ef9f
("drm/mgag200: Add support for a new rev of G200e"). In any event the
compiler is right in warning that testm/testn are possibly uninitalized
at this point, i.e. some change is needed no matter what.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Mathieu Larouche <mathieu.larouche@matrox.com>
---
v2: As pointed out by Mathieu, 1 needs to be added to both m and n when
    consuming them.
---
 drivers/gpu/drm/mgag200/mgag200_mode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 4.3-rc6/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ 4.3-rc6-mgag200-uninit/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -194,7 +194,7 @@ static int mga_g200se_set_plls(struct mg
 			}
 		}
 
-		fvv = pllreffreq * testn / testm;
+		fvv = pllreffreq * (n + 1) / (m + 1);
 		fvv = (fvv - 800000) / 50000;
 
 		if (fvv > 15)



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