Re: [PATCH v2] net/ice: fix statistics read error

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Nov 10, 2025 at 04:05:14PM +0800, Zhichao Zeng wrote:
> The statistics contain 40 bits. The lower 32 bits are read first, followed
> by the upper 8 bits.
> 
> In some cases, after reading the lower 32 bits, a carry occurs from
> the lower bits, which causes the final statistics to be incorrect.
> 
> This commit fixes this issue.
> 
> Fixes: a37bde56314d ("net/ice: support statistics")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Zhichao Zeng <zhichaox.zeng@intel.com>
> 
> ---
> v2: replace single retries with loops
> ---
>  drivers/net/intel/ice/ice_ethdev.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/intel/ice/ice_ethdev.c b/drivers/net/intel/ice/ice_ethdev.c
> index 4669eba7c7..016b25c63a 100644
> --- a/drivers/net/intel/ice/ice_ethdev.c
> +++ b/drivers/net/intel/ice/ice_ethdev.c
> @@ -6351,10 +6351,16 @@ ice_stat_update_40(struct ice_hw *hw,
>  		   uint64_t *stat)
>  {
>  	uint64_t new_data;
> +	uint32_t lo_old, hi, lo;
>  
> -	new_data = (uint64_t)ICE_READ_REG(hw, loreg);
> -	new_data |= (uint64_t)(ICE_READ_REG(hw, hireg) & ICE_8_BIT_MASK) <<
> -		    ICE_32_BIT_WIDTH;
> +	do {
> +		lo_old = ICE_READ_REG(hw, loreg);
> +		hi = ICE_READ_REG(hw, hireg);
> +		lo = ICE_READ_REG(hw, loreg);
> +	} while (lo_old > lo);
> +
> +	new_data = (uint64_t)lo;
> +	new_data |= (uint64_t)(hi & ICE_8_BIT_MASK) << ICE_32_BIT_WIDTH;
>  
>  	if (!offset_loaded)
>  		*offset = new_data;
> @@ -6363,10 +6369,8 @@ ice_stat_update_40(struct ice_hw *hw,
>  		*stat = new_data - *offset;
>  	else
>  		*stat = (uint64_t)((new_data +
> -				    ((uint64_t)1 << ICE_40_BIT_WIDTH)) -
> -				   *offset);
> -
> -	*stat &= ICE_40_BIT_MASK;
> +					((uint64_t)1 << ICE_32_BIT_WIDTH))
> +				   - *offset);

This part wasn't in v1, was it? It looks wrong to me, and the original code
looks correct. Given that offset and new_data should both be 40-bit
quantities, any wraparound would be at 40-bits rather than 32-bits no? Can
you explain why we would use a 32-bit shift here?

>  }
>  
>  /**
> -- 
> 2.34.1
>