net: stmmac: Don't use PHY loopback for selftests

Stmmac selftests validate the internal behaviour of the various IPs,
using local loopback. The current logic is relies on PHY-side local
loopback if a PHY is attached, with a fallback to MAC loopback
otherwise.

However, PHY loopback is currently fragile especially for stmmac that
may require RXC to be provided from the PHY. Some PHYs shutdown RXC
while in loopback, while others will report carrier off when in local
loopback. This also fails when using SFP setup with a module that embeds
a PHY, that may also fail to enter loopback.

MAC loopback is done at the GMII level on dwmac, allowing the internal
to be just as meaningful as PHY-loopback testing.

Let's simplify stmmac selftests by only relying on MAC-side local
loopback, which makes the selftests runnable on a wider HW variety.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260728155728.1193169-2-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions