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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Rob Herring , Krzysztof Kozlowski , Conor Dooley Cc: Yao Zi , netdev@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org Subject: Problematic understanding of phy-mode in Rockchip DWMAC driver Message-ID: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-ZohoMailClient: External Hi folks, I was looking through the RGMII delay setup logic found in rk_gmac_powerup() of dwmac-rk.c, and found its behavior is strange, switch (bsp_priv->phy_iface) { case PHY_INTERFACE_MODE_RGMII: dev_info(dev, "init for RGMII\n"); if (bsp_priv->ops->set_to_rgmii) bsp_priv->ops->set_to_rgmii(bsp_priv, bsp_priv->tx_delay, bsp_priv->rx_delay); break; case PHY_INTERFACE_MODE_RGMII_ID: dev_info(dev, "init for RGMII_ID\n"); if (bsp_priv->ops->set_to_rgmii) bsp_priv->ops->set_to_rgmii(bsp_priv, 0, 0); break; case PHY_INTERFACE_MODE_RGMII_RXID: dev_info(dev, "init for RGMII_RXID\n"); if (bsp_priv->ops->set_to_rgmii) bsp_priv->ops->set_to_rgmii(bsp_priv, bsp_priv->tx_delay, 0); break; case PHY_INTERFACE_MODE_RGMII_TXID: dev_info(dev, "init for RGMII_TXID\n"); if (bsp_priv->ops->set_to_rgmii) bsp_priv->ops->set_to_rgmii(bsp_priv, 0, bsp_priv->rx_delay); break; case PHY_INTERFACE_MODE_RMII: dev_info(dev, "init for RMII\n"); if (bsp_priv->ops->set_to_rmii) bsp_priv->ops->set_to_rmii(bsp_priv); break; default: dev_err(dev, "NO interface defined!\n"); } I don't think dwmac-rk.c does any fixup for phy_interface, so the MAC driver always connects the PHY with unmodified phy-mode. ethernet-controller.yaml states, > # Device Tree describes hardware, and in this case, it describes the > # PCB between the MAC and the PHY, if the PCB implements delays or > # not. So let's assume this is true for Rockchip's DWMAC glue, then the driver's behavior could be summarized as, phy-mode PCB delay Rockchip MAC delay PHY delay[1] rgmii TX & RX TX & RX TX & RX rgmii-id None None TX & RX rgmii-rxid TX TX RX rgmii-txid RX RX TX [1]: if available where only the "rgmii-id" case makes sense. Other cases come with 2ns delays added more than once, and would cause broken link. It looks like dwmac-rk.c considers "phy-mode" to represent MAC's delay configuration. If so, the table would look like, phy-mode PCB delay Rockchip MAC delay PHY delay[1] rgmii N/A TX & RX None rgmii-id N/A None TX & RX rgmii-txid N/A TX RX rgmii-rxid N/A RX TX all cases have the necessary 2ns delay provided for both TX and RX signals, however on-PCB delays made by traces couldn't be described at all. This idea is also proved by comments in Rockchip devicetrees, for example, rk3576-roc-pc.dts, &gmac0 { ... /* Use rgmii-rxid mode to disable rx delay inside Soc */ phy-mode = "rgmii-rxid"; }; It seems for Rockchip DWMAC driver, "phy-mode" doesn't follow the generic definition. Should we annotate in rockchip-dwmac.yaml to mention the different usage of the property, or update both the driver and devicetrees to align with ethernet-controller.yaml? The later would break compatibility with existing devicetrees since there are already 15 instances of "rgmii-rxid" found in arch/arm64/boot/dts/rockchip, but luckily most boards make use of "rgmii-id". I only did a brief search in lore but find no related discussion, please point out if there has already been messages around it, thanks. Best regards, Yao Zi