Some SoCs are just validated with the TX delay enabled. With commit
ca13b249f291 ("net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed
RGMII TX delay"), the network driver will patch the delay setting on the
fly assuming that the TX delay setting is fixed. In reality, the TX
delay is configurable and just skipped in the documentation. There are
bootloaders, which will disable the TX delay and this will lead to a
transmit path which doesn't add any delays at all.
Fix that by always writing the RGMII_ID setting and report an error for
unsupported RGMII delay modes.

This is safe to do and shouldn't break any boards in mainline because
the fixed delay is only introduced for gmii-sel compatibles which are
used together with the am65-cpsw-nuss driver and also contains the
commit above.

Fixes: ca13b249f291 ("net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed RGMII TX delay")
Signed-off-by: Michael Walle <mwalle@kernel.org>
---
v3:
 - simplify the logic. Thanks Matthias.
 - reworded the commit message

v2:
 - reject invalid PHY modes. Thanks Matthias.
 - add a paragraph to the commit message that this patch shouldn't
   break any existing boards. Thanks Andrew.

 drivers/phy/ti/phy-gmii-sel.c | 47 +++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 8 deletions(-)

diff --git a/drivers/phy/ti/phy-gmii-sel.c b/drivers/phy/ti/phy-gmii-sel.c
index ff5d5e29629f..50adabb867cb 100644
--- a/drivers/phy/ti/phy-gmii-sel.c
+++ b/drivers/phy/ti/phy-gmii-sel.c
@@ -34,6 +34,7 @@ enum {
 	PHY_GMII_SEL_PORT_MODE = 0,
 	PHY_GMII_SEL_RGMII_ID_MODE,
 	PHY_GMII_SEL_RMII_IO_CLK_EN,
+	PHY_GMII_SEL_FIXED_TX_DELAY,
 	PHY_GMII_SEL_LAST,
 };
 
@@ -127,6 +128,11 @@ static int phy_gmii_sel_mode(struct phy *phy, enum phy_mode mode, int submode)
 		goto unsupported;
 	}
 
+	/* With a fixed delay, some modes are not supported at all. */
+	if (soc_data->features & BIT(PHY_GMII_SEL_FIXED_TX_DELAY) &&
+	    rgmii_id != 0)
+		return -EINVAL;
+
 	if_phy->phy_if_mode = submode;
 
 	dev_dbg(dev, "%s id:%u mode:%u rgmii_id:%d rmii_clk_ext:%d\n",
@@ -210,25 +216,46 @@ struct phy_gmii_sel_soc_data phy_gmii_sel_soc_dm814 = {
 
 static const
 struct reg_field phy_gmii_sel_fields_am654[][PHY_GMII_SEL_LAST] = {
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x0, 0, 2), },
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x4, 0, 2), },
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x8, 0, 2), },
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0xC, 0, 2), },
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x10, 0, 2), },
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x14, 0, 2), },
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x18, 0, 2), },
-	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x1C, 0, 2), },
+	{
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x0, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x0, 4, 4),
+	}, {
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x4, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x4, 4, 4),
+	}, {
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x8, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x8, 4, 4),
+	}, {
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0xC, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0xC, 4, 4),
+	}, {
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x10, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x10, 4, 4),
+	}, {
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x14, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x14, 4, 4),
+	}, {
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x18, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x18, 4, 4),
+	}, {
+		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x1C, 0, 2),
+		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x1C, 4, 4),
+	},
 };
 
 static const
 struct phy_gmii_sel_soc_data phy_gmii_sel_soc_am654 = {
 	.use_of_data = true,
+	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
+		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
 	.regfields = phy_gmii_sel_fields_am654,
 };
 
 static const
 struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw5g_soc_j7200 = {
 	.use_of_data = true,
+	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
+		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
 	.regfields = phy_gmii_sel_fields_am654,
 	.extra_modes = BIT(PHY_INTERFACE_MODE_QSGMII) | BIT(PHY_INTERFACE_MODE_SGMII) |
 		       BIT(PHY_INTERFACE_MODE_USXGMII),
@@ -239,6 +266,8 @@ struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw5g_soc_j7200 = {
 static const
 struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw9g_soc_j721e = {
 	.use_of_data = true,
+	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
+		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
 	.regfields = phy_gmii_sel_fields_am654,
 	.extra_modes = BIT(PHY_INTERFACE_MODE_QSGMII) | BIT(PHY_INTERFACE_MODE_SGMII),
 	.num_ports = 8,
@@ -248,6 +277,8 @@ struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw9g_soc_j721e = {
 static const
 struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw9g_soc_j784s4 = {
 	.use_of_data = true,
+	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
+		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
 	.regfields = phy_gmii_sel_fields_am654,
 	.extra_modes = BIT(PHY_INTERFACE_MODE_QSGMII) | BIT(PHY_INTERFACE_MODE_SGMII) |
 		       BIT(PHY_INTERFACE_MODE_USXGMII),
-- 
2.39.5

On Tue, 19 Aug 2025 08:56:22 +0200, Michael Walle wrote:
> Some SoCs are just validated with the TX delay enabled. With commit
> ca13b249f291 ("net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed
> RGMII TX delay"), the network driver will patch the delay setting on the
> fly assuming that the TX delay setting is fixed. In reality, the TX
> delay is configurable and just skipped in the documentation. There are
> bootloaders, which will disable the TX delay and this will lead to a
> transmit path which doesn't add any delays at all.
> Fix that by always writing the RGMII_ID setting and report an error for
> unsupported RGMII delay modes.
> 
> [...]

Applied, thanks!

[1/1] phy: ti: gmii-sel: Always write the RGMII ID setting
      commit: a22d3b0d49d411e64ed07e30c2095035ecb30ed2

Best regards,
-- 
~Vinod

On Tue, 19 Aug 2025 08:56:22 +0200 Michael Walle wrote:
> v3:
>  - simplify the logic. Thanks Matthias.
>  - reworded the commit message

This was set to Not Applicable in our patchwork, IDK why.
Could you resend?

Hi,

On Fri Aug 22, 2025 at 3:18 AM CEST, Jakub Kicinski wrote:
> On Tue, 19 Aug 2025 08:56:22 +0200 Michael Walle wrote:
> > v3:
> >  - simplify the logic. Thanks Matthias.
> >  - reworded the commit message
>
> This was set to Not Applicable in our patchwork, IDK why.
> Could you resend?

Won't this patch be picked up by the linux-phy tree?

-michael

On Fri, 22 Aug 2025 08:45:33 +0200 Michael Walle wrote:
> On Fri Aug 22, 2025 at 3:18 AM CEST, Jakub Kicinski wrote:
> > On Tue, 19 Aug 2025 08:56:22 +0200 Michael Walle wrote:  
> > > v3:
> > >  - simplify the logic. Thanks Matthias.
> > >  - reworded the commit message  
> >
> > This was set to Not Applicable in our patchwork, IDK why.
> > Could you resend?  
> 
> Won't this patch be picked up by the linux-phy tree?

Ah, poops, you're right! Let me adjust our filters..

On 19/08/2025 08:56, Michael Walle wrote:
> Some SoCs are just validated with the TX delay enabled. With commit
> ca13b249f291 ("net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed
> RGMII TX delay"), the network driver will patch the delay setting on the
> fly assuming that the TX delay setting is fixed. In reality, the TX
> delay is configurable and just skipped in the documentation. There are
> bootloaders, which will disable the TX delay and this will lead to a
> transmit path which doesn't add any delays at all.
> Fix that by always writing the RGMII_ID setting and report an error for
> unsupported RGMII delay modes.
>
> This is safe to do and shouldn't break any boards in mainline because
> the fixed delay is only introduced for gmii-sel compatibles which are
> used together with the am65-cpsw-nuss driver and also contains the
> commit above.
>
> Fixes: ca13b249f291 ("net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed RGMII TX delay")
> Signed-off-by: Michael Walle <mwalle@kernel.org>

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime