linux-kernel - Re: [PATCH] net: wireless: rtlwifi: rtl8192de: hw.c: Cleaning up conjunction always evaluates to false

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Message-ID: <5393A7D0.2080700@lwfinger.net>
Date:	Sat, 07 Jun 2014 19:01:20 -0500
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Peter Wu <peter@...ensteyn.nl>
CC:	Chaoming Li <chaoming_li@...lsil.com.cn>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless@...r.kernel.org,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: wireless: rtlwifi: rtl8192de: hw.c: Cleaning up
 conjunction always evaluates to false

On 06/07/2014 10:24 AM, Rickard Strandqvist wrote:
> Hi!
>
> Yes, 0x3 was one of the most likely :)
> But wanted someone who knows the code better would be heard.
> All agreed? Then I do a new patch.
>
> Looks like it is the same error in the files below, I'll fix them all them to.
>
> rtl8192cu/hw.c:1363:    if ((bt_msr & 0xfc) == MSR_AP)
> rtl8192ce/hw.c:1209:    if ((bt_msr & 0xfc) == MSR_AP)
> rtl8188ee/hw.c:1234:    if ((bt_msr & 0xfc) == MSR_AP)
> rtl8192de/hw.c:1131:    if ((bt_msr & 0xfc) == MSR_AP)
>
>
> Best regards
> Rickard Strandqvist
>
>
> 2014-06-07 17:02 GMT+02:00 Peter Wu <peter@...ensteyn.nl>:
>> On Saturday 07 June 2014 16:30:19 Rickard Strandqvist wrote:
>>> Expression '(X & 0xfc) == 0x3' is always false
>>
>> While this is true, I believe that some other mistake is made.
>>
>>> I chose to remove this code, because it will not make any difference.
>>> But obviously it is rather a properly designed if statement that is needed.
>>>
>>> This was partly found using a static code analysis program called cppcheck.
>>>
>>> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
>>> ---
>>>   drivers/net/wireless/rtlwifi/rtl8192de/hw.c |    5 +----
>>>   1 file changed, 1 insertion(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/net/wireless/rtlwifi/rtl8192de/hw.c b/drivers/net/wireless/rtlwifi/rtl8192de/hw.c
>>> index 2b08671..a1520d5 100644
>>> --- a/drivers/net/wireless/rtlwifi/rtl8192de/hw.c
>>> +++ b/drivers/net/wireless/rtlwifi/rtl8192de/hw.c
>>> @@ -1128,10 +1128,7 @@ static int _rtl92de_set_media_status(struct ieee80211_hw *hw,
>>>        }
>>>        rtl_write_byte(rtlpriv, REG_CR + 2, bt_msr);
>>>        rtlpriv->cfg->ops->led_control(hw, ledaction);
>>> -     if ((bt_msr & 0xfc) == MSR_AP)
>>
>> If you look a few lines up, then you see that bt_msr is OR-ed with MSR_AP
>> for AP interfaces. The 0xfc should be 0x03, see other drivers for example:
>>
>> rtl8723ae/hw.c:1112:    if ((bt_msr & 0x03) == MSR_AP)
>> rtl8723be/hw.c:1200:    if ((bt_msr & 0x03) == MSR_AP)
>> rtl8192cu/hw.c:1363:    if ((bt_msr & 0xfc) == MSR_AP)
>> rtl8192ce/hw.c:1209:    if ((bt_msr & 0xfc) == MSR_AP)
>> rtl8188ee/hw.c:1234:    if ((bt_msr & 0xfc) == MSR_AP)
>> rtl8192de/hw.c:1131:    if ((bt_msr & 0xfc) == MSR_AP)
>>
>>> -             rtl_write_byte(rtlpriv, REG_BCNTCFG + 1, 0x00);
>>> -     else
>>> -             rtl_write_byte(rtlpriv, REG_BCNTCFG + 1, 0x66);
>>> +     rtl_write_byte(rtlpriv, REG_BCNTCFG + 1, 0x66);
>>>        return 0;
>>>   }

Peter,

As you have learned here, automatically making changes suggested by some tool 
may convert a visible bug into one that is invisible, and only found by a 
detailed line-by-line examination of the code, and that is unlikely to happen. 
Please be careful.

 From everything I see, the test in all drivers should be

	if ((bt_msr & MSR_AP) == MSR_AP)

Larry

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