netdev - RE: [Intel-wired-lan] [PATCH iwl-next v2 5/5] ixgbe: drop unnecessary constant casts to u16

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Message-ID: <IA3PR11MB8986B9D474298EEEFA3C57E5E54EA@IA3PR11MB8986.namprd11.prod.outlook.com>
Date: Tue, 8 Jul 2025 08:54:56 +0000
From: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>
To: Jacek Kowalski <jacek@...ekk.info>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "Kitszel, Przemyslaw"
	<przemyslaw.kitszel@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>
CC: "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [Intel-wired-lan] [PATCH iwl-next v2 5/5] ixgbe: drop unnecessary
 constant casts to u16



> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf
> Of Jacek Kowalski
> Sent: Tuesday, July 8, 2025 10:19 AM
> To: Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@...el.com>; Andrew Lunn
> <andrew+netdev@...n.ch>; David S. Miller <davem@...emloft.net>; Eric
> Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo
> Abeni <pabeni@...hat.com>; Simon Horman <horms@...nel.org>
> Cc: intel-wired-lan@...ts.osuosl.org; netdev@...r.kernel.org
> Subject: [Intel-wired-lan] [PATCH iwl-next v2 5/5] ixgbe: drop
> unnecessary constant casts to u16
> 
> Remove unnecessary casts of constant values to u16.
> Let the C type system do it's job.
> 
> Signed-off-by: Jacek Kowalski <Jacek@...ekk.info>
> Suggested-by: Simon Horman <horms@...nel.org>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_common.c | 2 +-
>  drivers/net/ethernet/intel/ixgbe/ixgbe_x540.c   | 2 +-
>  drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c   | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> index 4ff19426ab74..cb28c26e12f2 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> @@ -1739,7 +1739,7 @@ int ixgbe_calc_eeprom_checksum_generic(struct
> ixgbe_hw *hw)
>  		}
>  	}
> 
> -	checksum = (u16)IXGBE_EEPROM_SUM - checksum;
> +	checksum = IXGBE_EEPROM_SUM - checksum;
> 
Can't lead to different results, especially when:
checksum > IXGBE_EEPROM_SUM → the result becomes negative in int, and narrowing to u16 causes unexpected wraparound?

With this patch you are changing the semantics of the code - from explicit 16bit arithmetic to full int implicit promotion which can be error-prone or compiler-dependent /* for different targets */.

>  	return (int)checksum;
>  }
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_x540.c
> b/drivers/net/ethernet/intel/ixgbe/ixgbe_x540.c
> index c2353aed0120..07c4a42ea282 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_x540.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_x540.c
> @@ -373,7 +373,7 @@ static int ixgbe_calc_eeprom_checksum_X540(struct
> ixgbe_hw *hw)
>  		}
>  	}
> 
> -	checksum = (u16)IXGBE_EEPROM_SUM - checksum;
> +	checksum = IXGBE_EEPROM_SUM - checksum;
> 
>  	return (int)checksum;
>  }
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c
> b/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c
> index bfa647086c70..0cc80ce8fcdc 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c
> @@ -1060,7 +1060,7 @@ static int ixgbe_calc_checksum_X550(struct
> ixgbe_hw *hw, u16 *buffer,
>  			return status;
>  	}
> 
> -	checksum = (u16)IXGBE_EEPROM_SUM - checksum;
> +	checksum = IXGBE_EEPROM_SUM - checksum;
> 
>  	return (int)checksum;
>  }
> --
> 2.47.2