Re: [PATCH] staging: rtl8723bs: fix underflow logic in swing index calculations

[Nikolay Kulikov <nikolayof23@gmail.com>]

On Wed, Jul 29, 2026 at 10:57:07PM +0530, Mohit Mishra wrote:
> In ODM_TxPwrTrackSetPwr_8723B(), the baseband swing index variables
> Final_OFDM_Swing_Index and Final_CCK_Swing_Index are declared as u8.
> However, their calculation adds Absolute_OFDMSwingIdx, which is a signed
> 8-bit integer (s8) and can be negative:
> 
>     Final_OFDM_Swing_Index = pDM_Odm->DefaultOfdmIndex +
>                              pDM_Odm->Absolute_OFDMSwingIdx[RFPath];
> 
> If the resulting sum is negative, it underflows under u8 rules (e.g. -5
> becomes 251). This causes the lower-limit checks (e.g. <= 0) to fail,
> and in MIX_MODE causes the logic to execute the "BBSwing higher than limit"
> branch instead of capping to 0.
> 
> Additionally, in BBSWING mode, the check for CCK underflow mistakenly
> examines the static struct member pDM_Odm->BbSwingIdxCck instead of the
> newly calculated Final_CCK_Swing_Index:
> 
>     else if (pDM_Odm->BbSwingIdxCck <= 0)
> 
> Fix this by changing both swing index variable types to int to enable
> signed math and correct branch selection (aligning with the TODO item to
> convert remaining unusual variable types). Update the CCK check in
> BBSWING mode to examine Final_CCK_Swing_Index.
> 
> Note: The fix is scoped to the calculation and branching logic. When
> passed downstream to setIqkMatrix_8723B() and setCCKFilterCoefficient(),
> the values are already clamped within [0, 42], fitting safely in u8.

There is no need to try to fix the check in BBSWING mode - it never
executes and can be removed.
The ODM_TxPwrTrackSetPwr_8723B() function is always called with 'Method'
set to 'MIX_MODE' (see hal/HalPhyRf.c, lines 252 and 255).


Thanks,
Nikolay

> 
> Compile-tested only; no hardware available for testing.
> 
> Signed-off-by: Mohit Mishra <mishraloopmohit@gmail.com>
> ---
>  drivers/staging/rtl8723bs/hal/HalPhyRf_8723B.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/rtl8723bs/hal/HalPhyRf_8723B.c b/drivers/staging/rtl8723bs/hal/HalPhyRf_8723B.c
> index 6c5f56d5a1f4..4e89847700f3 100644
> --- a/drivers/staging/rtl8723bs/hal/HalPhyRf_8723B.c
> +++ b/drivers/staging/rtl8723bs/hal/HalPhyRf_8723B.c
> @@ -160,8 +160,8 @@ void ODM_TxPwrTrackSetPwr_8723B(
>  	u8 PwrTrackingLimit_OFDM = 34; /* 0dB */
>  	u8 PwrTrackingLimit_CCK = 28; /* 2dB */
>  	u8 TxRate = 0xFF;
> -	u8 Final_OFDM_Swing_Index = 0;
> -	u8 Final_CCK_Swing_Index = 0;
> +	int Final_OFDM_Swing_Index = 0;
> +	int Final_CCK_Swing_Index = 0;
>  
>  	{
>  		u16 rate = *(pDM_Odm->pForcedDataRate);
> @@ -217,7 +217,7 @@ void ODM_TxPwrTrackSetPwr_8723B(
>  
>  		if (Final_CCK_Swing_Index >= CCK_TABLE_SIZE)
>  			Final_CCK_Swing_Index = CCK_TABLE_SIZE-1;
> -		else if (pDM_Odm->BbSwingIdxCck <= 0)
> +		else if (Final_CCK_Swing_Index <= 0)
>  			Final_CCK_Swing_Index = 0;
>  
>  		setIqkMatrix_8723B(pDM_Odm, Final_OFDM_Swing_Index, RFPath,
> -- 
> 2.43.0
> 
>