Re: [PATCH] net: stmmac: guard FCS stripping against runt frames

[Andrew Lunn]

On Thu, Sep 24, 2026 at 10:51:11AM -0300, Aldo Ariel wrote:
> Hi Andrew, Lorenzo,
> 
> Fair point on the subject — the trigger is not limited to runt frames.
>  
> The FCS stripping in stmmac_rx() at lines 5810-5817 runs on every
> last-segment descriptor regardless of total frame size:
> 
>     if (likely(!(status & rx_not_ls))) {
>         if (buf2_len) {
>             buf2_len -= ETH_FCS_LEN;
>         } else if (buf1_len) {
>             buf1_len -= ETH_FCS_LEN;
>         }
>     }      
>        
> For a multi-descriptor frame, the last descriptor's buf2_len or
> buf1_len carries only the tail of the frame. With the default
> dma_buf_sz = BUF_SIZE_2KiB for MTU 1500, a 4097-byte frame splits as:

Is the MTU programmed into the hardware? Will it even try to transfer
an 4097 octet frame when the MTU is configured to 1500?

   Andrew