From: Arınç ÜNAL arinc.unal@arinc9.com

commit f490c492e946d8ffbe65ad4efc66de3c5ede30a4 upstream.

On MT7530, the HT_XTAL_FSEL field of the HWTRAP register stores a 2-bit value that represents the frequency of the crystal oscillator connected to the switch IC. The field is populated by the state of the ESW_P4_LED_0 and ESW_P4_LED_0 pins, which is done right after reset is deasserted.

ESW_P4_LED_0 ESW_P3_LED_0 Frequency ----------------------------------------- 0 0 Reserved 0 1 20MHz 1 0 40MHz 1 1 25MHz

On MT7531, the XTAL25 bit of the STRAP register stores this. The LAN0LED0 pin is used to populate the bit. 25MHz when the pin is high, 40MHz when it's low.

These pins are also used with LEDs, therefore, their state can be set to something other than the bootstrapping configuration. For example, a link may be established on port 3 before the DSA subdriver takes control of the switch which would set ESW_P3_LED_0 to high.

Currently on mt7530_setup() and mt7531_setup(), 1000 - 1100 usec delay is described between reset assertion and deassertion. Some switch ICs in real life conditions cannot always have these pins set back to the bootstrapping configuration before reset deassertion in this amount of delay. This causes wrong crystal frequency to be selected which puts the switch in a nonfunctional state after reset deassertion.

The tests below are conducted on an MT7530 with a 40MHz crystal oscillator by Justin Swartz.

With a cable from an active peer connected to port 3 before reset, an incorrect crystal frequency (0b11 = 25MHz) is selected:

[1] [3] [5] : : : _____________________________ __________________ ESW_P4_LED_0 |_______| _____________________________ ESW_P3_LED_0 |__________________________

: : : : : : [4]...: : : [2]................:

[1] Reset is asserted. [2] Period of 1000 - 1100 usec. [3] Reset is deasserted. [4] Period of 315 usec. HWTRAP register is populated with incorrect XTAL frequency. [5] Signals reflect the bootstrapped configuration.

Increase the delay between reset_control_assert() and reset_control_deassert(), and gpiod_set_value_cansleep(priv->reset, 0) and gpiod_set_value_cansleep(priv->reset, 1) to 5000 - 5100 usec. This amount ensures a higher possibility that the switch IC will have these pins back to the bootstrapping configuration before reset deassertion.

With a cable from an active peer connected to port 3 before reset, the correct crystal frequency (0b10 = 40MHz) is selected:

[1] [2-1] [3] [5] : : : : _____________________________ __________________ ESW_P4_LED_0 |_______| ___________________ _______ ESW_P3_LED_0 |_________| |__________________

: : : : : : [2-2]...: [4]...: [2]................:

[1] Reset is asserted. [2] Period of 5000 - 5100 usec. [2-1] ESW_P3_LED_0 goes low. [2-2] Remaining period of 5000 - 5100 usec. [3] Reset is deasserted. [4] Period of 310 usec. HWTRAP register is populated with bootstrapped XTAL frequency. [5] Signals reflect the bootstrapped configuration.

ESW_P3_LED_0 low period before reset deassertion:

5000 usec - 5100 usec TEST RESET HOLD # (usec) --------------------- 1 5410 2 5440 3 4375 4 5490 5 5475 6 4335 7 4370 8 5435 9 4205 10 4335 11 3750 12 3170 13 4395 14 4375 15 3515 16 4335 17 4220 18 4175 19 4175 20 4350

Min 3170 Max 5490

Median 4342.500 Avg 4466.500

Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch") Fixes: c288575f7810 ("net: dsa: mt7530: Add the support of MT7531 switch") Co-developed-by: Justin Swartz justin.swartz@risingedge.co.za Signed-off-by: Justin Swartz justin.swartz@risingedge.co.za Signed-off-by: Arınç ÜNAL arinc.unal@arinc9.com Signed-off-by: David S. Miller davem@davemloft.net --- Hi.

I've adjusted the patch to suit stable trees by removing the last paragraph on the patch log. This is an important patch that should be backported to stable releases. Please apply to 6.8, 6.7, 6.6, 6.1, and 5.15 stable trees. --- drivers/net/dsa/mt7530.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c index 3c1f657593a8..9c9a592c053e 100644 --- a/drivers/net/dsa/mt7530.c +++ b/drivers/net/dsa/mt7530.c @@ -2243,11 +2243,11 @@ mt7530_setup(struct dsa_switch *ds) */ if (priv->mcm) { reset_control_assert(priv->rstc); - usleep_range(1000, 1100); + usleep_range(5000, 5100); reset_control_deassert(priv->rstc); } else { gpiod_set_value_cansleep(priv->reset, 0); - usleep_range(1000, 1100); + usleep_range(5000, 5100); gpiod_set_value_cansleep(priv->reset, 1); }

@@ -2449,11 +2449,11 @@ mt7531_setup(struct dsa_switch *ds) */ if (priv->mcm) { reset_control_assert(priv->rstc); - usleep_range(1000, 1100); + usleep_range(5000, 5100); reset_control_deassert(priv->rstc); } else { gpiod_set_value_cansleep(priv->reset, 0); - usleep_range(1000, 1100); + usleep_range(5000, 5100); gpiod_set_value_cansleep(priv->reset, 1); }

--- base-commit: e8f897f4afef0031fe618a8e94127a0934896aba change-id: 20240318-b4-for-stable-f486c9ff8d86

Best regards,