6.6-stable review patch. If anyone has any objections, please let me know.
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From: Jacky Chou jacky_chou@aspeedtech.com
[ Upstream commit d1a1a4bade4b20c0858d0b2f81d2611de055f675 ]
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 jacky_chou@aspeedtech.com Reviewed-by: Andrew Lunn andrew@lunn.ch Link: https://patch.msgid.link/20251211-aspeed_mdio_add_dummy_read-v3-1-3828688690... Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 c727103c8b05..339198a4dbc0 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,