From nobody Fri Dec 19 16:38:13 2025 Received: from TWMBX01.aspeed.com (mail.aspeedtech.com [211.20.114.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 136A91684B4; Fri, 5 Dec 2025 01:37:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=211.20.114.72 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764898658; cv=none; b=O4ffIj0mG0U23cAV2WWme2iyukoDzC8my2dNnLA8XAiYV/1+/fL2CWHcW54NaOiS7OjI6nbTLebODvhyFK7Wxo9NQpgouhOYJnaECIQAgK0y1pALNU1r2H/ndBpkRiKTvedpMruwl0CU9wSxtzHkzZx6alIEUdrVU7v5OeUBcFY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764898658; c=relaxed/simple; bh=S7YMglq8xDZ86NvHllMwMpita0VXT5NdJ+3b28QfTZA=; h=From:Date:Subject:MIME-Version:Content-Type:Message-ID:To:CC; b=qbsNswfEWEsl2ZzjUXXEX8Z6prsxFlLRpyK+sOOycnif4iW9+bFcRjgi/myVUE3TNfEnnE9RdtSD0wTbFNiLEi6r/jghNWodXoFku0HD+BgC4Ag3XdeyGZWC+cI0h2jsh6bwykIIBPWKeGBNlrdTe3dfyZX/ifZITBNYZzmsgPc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=aspeedtech.com; spf=pass smtp.mailfrom=aspeedtech.com; arc=none smtp.client-ip=211.20.114.72 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=aspeedtech.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=aspeedtech.com Received: from TWMBX01.aspeed.com (192.168.0.62) by TWMBX01.aspeed.com (192.168.0.62) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1748.10; Fri, 5 Dec 2025 09:37:27 +0800 Received: from [127.0.1.1] (192.168.10.13) by TWMBX01.aspeed.com (192.168.0.62) with Microsoft SMTP Server id 15.2.1748.10 via Frontend Transport; Fri, 5 Dec 2025 09:37:27 +0800 From: Jacky Chou Date: Fri, 5 Dec 2025 09:37:22 +0800 Subject: [PATCH net-next] net: mdio: aspeed: add dummy read to avoid read-after-write issue Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-ID: <20251205-aspeed_mdio_add_dummy_read-v1-1-60145ae20ea7@aspeedtech.com> X-B4-Tracking: v=1; b=H4sIAFE3MmkC/x3MQQqDMBAF0KvIrBswwUDbq5QSQv9vO4tESaxYx LsbXL7N26SyKKvcu00KF6065gZ76eT1jflDo2gW1ztvXe9NrBOJkKBjiEDAL6V/KIww8FdYDrf BOkgLpsK3rmf+kMzZZK6zPPf9AIb4G/R2AAAA X-Change-ID: 20251205-aspeed_mdio_add_dummy_read-d58d1e49412d To: Andrew Lunn , Heiner Kallweit , Russell King , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Joel Stanley , Andrew Jeffery CC: , , , , Jacky Chou X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1764898647; l=1685; i=jacky_chou@aspeedtech.com; s=20251031; h=from:subject:message-id; bh=S7YMglq8xDZ86NvHllMwMpita0VXT5NdJ+3b28QfTZA=; b=Ps7Hi70frz0jQRXPVvsI7ldWRC/vUIB2+MlTS0A8qMwi2htDxw+IuUKtQFWJ/D4fb+S5YT/WU +6J+70lg37kB2/KkYTcqTd2EYPL6bmdnjhSrYXB//9EmSRmeEb1bkfX X-Developer-Key: i=jacky_chou@aspeedtech.com; a=ed25519; pk=8XBx7KFM1drEsfCXTH9QC2lbMlGU4XwJTA6Jt9Mabdo= 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. Signed-off-by: Jacky Chou --- drivers/net/mdio/mdio-aspeed.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/net/mdio/mdio-aspeed.c b/drivers/net/mdio/mdio-aspeed.c index e55be6dc9ae7..00e61b922876 100644 --- a/drivers/net/mdio/mdio-aspeed.c +++ b/drivers/net/mdio/mdio-aspeed.c @@ -62,6 +62,12 @@ static int aspeed_mdio_op(struct mii_bus *bus, u8 st, u8= op, u8 phyad, u8 regad, | FIELD_PREP(ASPEED_MDIO_DATA_MIIRDATA, data); =20 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. + */ + (void)ioread32(ctx->base + ASPEED_MDIO_CTRL); =20 return readl_poll_timeout(ctx->base + ASPEED_MDIO_CTRL, ctrl, !(ctrl & ASPEED_MDIO_CTRL_FIRE), --- base-commit: 8f7aa3d3c7323f4ca2768a9e74ebbe359c4f8f88 change-id: 20251205-aspeed_mdio_add_dummy_read-d58d1e49412d Best regards, --=20 Jacky Chou