The Aspeed MDIO controller may return incorrect data when a read operation follows immediately after a write. Due to a controller bug, the subsequent read can latch stale data, causing the polling logic to terminate earlier than expected. To work around this hardware issue, insert a dummy read after each write operation. This ensures that the next actual read returns the correct data and prevents premature polling exit. This workaround has been verified to stabilize MDIO transactions on affected Aspeed platforms. Fixes: f160e99462c6 ("net: phy: Add mdio-aspeed") Signed-off-by: Jacky Chou --- Changes in v3: - Remove (void) - Link to v2: https://lore.kernel.org/r/20251209-aspeed_mdio_add_dummy_read-v2-1-5f6061641989@aspeedtech.com Changes in v2: - Updated the Fixes: tag - Link to v1: https://lore.kernel.org/r/20251208-aspeed_mdio_add_dummy_read-v1-1-0a1861ad2161@aspeedtech.com --- drivers/net/mdio/mdio-aspeed.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/net/mdio/mdio-aspeed.c b/drivers/net/mdio/mdio-aspeed.c index e55be6dc9ae7..d6b9004c61dc 100644 --- a/drivers/net/mdio/mdio-aspeed.c +++ b/drivers/net/mdio/mdio-aspeed.c @@ -63,6 +63,13 @@ static int aspeed_mdio_op(struct mii_bus *bus, u8 st, u8 op, u8 phyad, u8 regad, iowrite32(ctrl, ctx->base + ASPEED_MDIO_CTRL); + /* Workaround for read-after-write issue. + * The controller may return stale data if a read follows immediately + * after a write. A dummy read forces the hardware to update its + * internal state, ensuring that the next real read returns correct data. + */ + ioread32(ctx->base + ASPEED_MDIO_CTRL); + return readl_poll_timeout(ctx->base + ASPEED_MDIO_CTRL, ctrl, !(ctrl & ASPEED_MDIO_CTRL_FIRE), ASPEED_MDIO_INTERVAL_US, --- base-commit: 6bcb7727d9e612011b70d64a34401688b986d6ab change-id: 20251208-aspeed_mdio_add_dummy_read-587ab8808817 Best regards, -- Jacky Chou