On Sun, Nov 29, 2020 at 11:23:59AM +0100, Jean Pihet wrote:

Some ethernet controllers (e.g. TI CPSW) pad the frames to a minimum
of 64 bytes before the FCS is appended. This causes an issue with the
KSZ tail tag which could not be the last byte before the FCS.
Solve this by padding the frame to 64 bytes minus the tail tag size,
before the tail tag is added and the frame is passed for transmission.

Hi Jean

what tree is this based on? Have you seen

commit 88fda8eefd9a7a7175bf4dad1d02cc0840581111
Author: Christian Eggers [off-list ref]
Date:   Sun Nov 1 21:16:10 2020 +0200

    net: dsa: tag_ksz: don't allocate additional memory for padding/tagging
    
    The caller (dsa_slave_xmit) guarantees that the frame length is at least
    ETH_ZLEN and that enough memory for tail tagging is available.