On Tue, Feb 3, 2026 at 8:58 AM Heinrich Toews [off-list ref] wrote:

Hi Rob,

On Fri, Jan 30, 2026 at 01:46:52PM -0800, Tim Harvey wrote:

quoted

quoted

diff --git a/drivers/net/dsa/microchip/ksz_common.c

b/drivers/net/dsa/microchip/ksz_common.c
index e5fa1f5fc09b3..bef8ec51d9483 100644

--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c

@@ -815,6 +815,9 @@  static const u16 ksz9477_regs[] = {
  [PTP_RTC_SEC] = 0x0508,
  [PTP_SUBNANOSEC_RATE] = 0x050C,
  [PTP_MSG_CONF1] = 0x0514,
+ [P_PHY_MMD_SETUP] = 0x011A,
+ [P_PHY_MMD_DATA] = 0x011C,
+ [P_PHY_DIGITAL_DEBUG_3] = 0x013C,
 };

@@ -3241,6 +3244,14 @@  static u32 ksz_get_phy_flags(struct dsa_switch

*ds, int port)
  if (!port)
  return MICREL_KSZ8_P1_ERRATA;
  break;
+ case KSZ9477_CHIP_ID:
+ /* KSZ9477S Errata DS80000754F
+ *
+ * Module 19: Single-LED Mode Setting Requires Two Register Writes
+ *   The PHY Port LEDx_0 pin does not go low in the presence of link
+ *   activity when Single-LED Mode is selected in the MMD LED Mode Register.
+ */
+ return MICREL_KSZ9_LED_ERRATA;
  }

Hi Heinrich,

Thanks for doing this. I have two boards I work with that have a
KSZ9897S switch and use single-led mode (imx8mp-venice-gw74xx.dts and
imx8mm-venice-gw7901.dts) that suffer from this issue. In my scenario
I take care of this in the bootloader but when ksz9477_reset_switch()
is called and sets the SW_RESET bit of REG_SW_OPERATION it resets all
registers and reverts to tri-color dual-led mode thus we really do
need a dt prop and handling for this.

I agree. To support these use cases, a specific Device Tree property
would be the right thing here.

quoted

You can add the errata for KSZ9897 as well here:
+       case KSZ9897_CHIP_ID:
+               /* KSZ9897S Errata DS80000759F: Module 18 */
+               return MICREL_KSZ9_LED_ERRATA;

And because this errata applies to multiple chips it's probably best
to describe the workaround once and refer to the errata # in the cases
statements.

I did some research on this and it seems that nearly all members of the
KSZ9xxx series are affected, including:

KSZ9477 / KSZ9897 / KSZ9896
KSZ9567 / KSZ8567 / KSZ9893
KSZ9563 / KSZ8563 / KSZ8565

So MICREL_KSZ9_LED_ERRATA should be enabled for these CHIP_IDs.

quoted

quoted

+static void ksz_enable_single_led_mode(struct ksz_device *dev, int
port, struct phy_device *phydev)
+{
+ const u16 *regs = dev->info->regs;
+
+ ksz_pwrite16(dev, port, regs[P_PHY_MMD_SETUP], 0x0002); /* Set up
register address for MMD */
+ ksz_pwrite16(dev, port,  regs[P_PHY_MMD_DATA], 0x0000); /* Select
Register 00h of MMD */
+ ksz_pwrite16(dev, port, regs[P_PHY_MMD_SETUP], 0x4002); /* Select
register data for MMD */
+ ksz_pwrite16(dev, port,  regs[P_PHY_MMD_DATA], 0x0011); /* Write
value 0011h to MMD */

These are wrong: The MMD_SETUP and MMD_DATA regs you are using here
0x011a and 0x11c are actually 0xN11a 0x 0xN11c (where N is the port)
so they port specific so the above only would set them for port0.
Because these registers correspond to standardPHY register 0x0d and
0x0e which are defined in mii.h you can just use those.

What you want here is to use ksz_phy_write16 on the port which will
call the chip-specific w_phy which will handle writing to the port
specific register:
ksz_phy_write16(dev, port, MII_MMD_CTRL, 0x02);
ksz_phy_write16(dev, port, MII_MMD_DATA, 0x00);
ksz_phy_write16(dev, port, MII_MMD_CTRL, MII_MMD_CTRL_NOINCR | 0x02);
ksz_phy_write16(dev, port, MII_MMD_DATA, 0x10);

I added debug output and tested my setup on all 4 external ports and it
works:

ksz-switch spi1.0: ksz_pwrite16: port: 1, offset: 0x011a, data: 0x0002
ksz-switch spi1.0: ksz_write16: reg: 0x0000211a, value: 0x0002
                                                          ^^^^
                                                          The port index
                                                          is set
                                                          correctly.

[...]

ksz-switch spi1.0: ksz_pwrite16: port: 2, offset: 0x011a, data: 0x0002
ksz-switch spi1.0: ksz_write16: reg: 0x0000311a, value: 0x0002
                                                          ^^^^
                                                          The same here
                                                          on port 2.

Is see activity on the leds connected to LEDx_0.

Hi Heinrich,

My apologies - you are correct. I accidentally missed the hunk where
you set your registers in ksz9477_regs causing it to not work for me.

ksz9477_get_port_addr() is adding the port index by PORT_CTRL_ADDR(port, offset).

But since I'm accessing PHY registers here, I'll switch to ksz_phy_write16() in v2.

Yes, that would be best as you would no longer need to add custom registers.

I have:

        ksz_phy_write16(dev->ds, port, MII_MMD_CTRL, 0x0002);
        ksz_phy_write16(dev->ds, port,  MII_MMD_DATA, 0x0000);
        ksz_phy_write16(dev->ds, port, MII_MMD_CTRL,
MII_MMD_CTRL_NOINCR | 0x02);
        ksz_phy_write16(dev->ds, port,  MII_MMD_DATA, 0x0010); /* set bit 4 */
        /* LED_ERRATA requires writing 0xfa00 to Debug Register 3 (PHY
register 0x1e) */
        if (phydev->dev_flags & MICREL_KSZ9_LED_ERRATA)
                ksz_phy_write16(dev->ds, port, 0x1e, 0xfa00);

I look forward to seeing your next submission.

Best Regards,

Tim

quoted

Note on that last one, the errata says to write 0x11 but that's a typo
as if you read closely it says 'setting bit 4' and looking at the
datasheet bit0 is reserved, so the 0x11 should be 0x10.

Yes, you're right. I remember seeing it before. Thanks.

quoted

Similarly the errata specifies this as PHY register 0x1E (which is a
vendor specific register so not defined in mii.h):

ksz_phy_write16(dev, port, 0x1e, 0xfa00);

May be I should add a local macro define for it.

quoted

Your original patch doesn't work in my case (maybe it worked for you
because you were trying to address port0?). With the above changes the
LED's are properly configured on my boards.

Okay. But I don't really understand why its not working in your
case.

Thanks for you're feedback.

Regards,
Heinrich.