Recently I am working on switch driver porting with Microchip ksz9897 to support 7 ports in kernel 5.10 DSA. The switch port 0 to 4 are ports which connect to RJ45, port 5 connect to CPU (internal PHYs) via MII, port 6 connect to ksz8081 via RMII (external PHYs).
From hardware point of view port 6 has no difference to port 0 to 4 except an additional PHYs however I am not able to test ping on port 6. Luckily port 6 can be verified without driver, and this makes me believe that something go wrong in Microchip DSA driver.
Attachment is the patch to have switch driver support port 6 with external PHYs. However after speaking to DSA kernel maintainer they talk to me that switch driver should not assume external PHYs exist.
On Fri, Dec 17, 2021 at 02:53:15AM +0000, KARL_TSOU (鄒磊) wrote:
> The Microchip switch ksz9897 support 7 physical port, port 0/1/2/3/4 connect to standard RJ45, port5 connect to PHY via MII to CPU and port6 connect to PHY via RMII (PHY ksz8081) on my custom board.
> I am facing a problem that I am not able to verify port6 via ping command even though the link is up, port 0/1/2/3/4 are all works fine by verifying with ping command expect port6
>
> When I go through port initialization code, a "if condition" below that aren't included port6 initialization.
This initialization is for the internal PHYs. They have to
exist. External PHYs the switch driver should not assume exist. You
normally connect to the CPU directly, not via back to back PHYs. Any
there could be boards which use port 6 direct to the CPU without a
PHY. So this change as is, is wrong.
You should be using a phy-handle in DT for port6, or port5, to
indicate if a PHY is connected to the port. Do you have this property?
If anyone's hardware switch design support port 6 that encounter port 6 aren't working problem please merge the patch.
