Commit d1a1a4ba authored by Jacky Chou's avatar Jacky Chou Committed by Paolo Abeni
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net: mdio: aspeed: add dummy read to avoid read-after-write issue 



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: f160e994 ("net: phy: Add mdio-aspeed")
Signed-off-by: default avatarJacky Chou <jacky_chou@aspeedtech.com>
Reviewed-by: default avatarAndrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20251211-aspeed_mdio_add_dummy_read-v3-1-382868869004@aspeedtech.com


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent bf4172bd

drivers/net/mdio/mdio-aspeed.c

+7 −0
Original line number Diff line number Diff line
@@ -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,