On Wed, Jul 17, 2019 at 02:57:39PM +0200, Simon Horman wrote:
> * According to the R-Car Gen3 Hardware Manual Errata for Rev 1.00 of
>   August 24, 2018, the TX clock internal delay mode isn't supported
>   on R-Car E3 (r8a77990) and D3 (r8a77995).
> 
> * TX clock internal delay mode is required for reliable 1Gbps communication
>   using the KSZ9031RNX phy present on the Ebisu and Draak boards.
> 
> Thus, the E3 based Ebisu and D3 based Draak boards reliably use 1Gbps and
> the speed should be limited to 100Mbps.
> 
> Based on work by Kazuya Mizuguchi.
> 
> Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

What about adding a short comment explaining the situation?