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95 lines
3.0 KiB
Diff
95 lines
3.0 KiB
Diff
From de16cf680331cd0bd7db97c3f8d376f5eac39cae Mon Sep 17 00:00:00 2001
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From: Justin Swartz <justin.swartz@risingedge.co.za>
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Date: Tue, 5 Mar 2024 06:39:51 +0200
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Subject: [PATCH 28/30] net: dsa: mt7530: disable LEDs before reset
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Disable LEDs just before resetting the MT7530 to avoid
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situations where the ESW_P4_LED_0 and ESW_P3_LED_0 pin
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states may cause an unintended external crystal frequency
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to be selected.
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The HT_XTAL_FSEL (External Crystal Frequency Selection)
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field of HWTRAP (the Hardware Trap register) stores a
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2-bit value that represents the state of the ESW_P4_LED_0
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and ESW_P4_LED_0 pins (seemingly) sampled just after the
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MT7530 has been reset, as:
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ESW_P4_LED_0 ESW_P3_LED_0 Frequency
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-----------------------------------------
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0 1 20MHz
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1 0 40MHz
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1 1 25MHz
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The value of HT_XTAL_FSEL is bootstrapped by pulling
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ESW_P4_LED_0 and ESW_P3_LED_0 up or down accordingly,
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but:
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if a 40MHz crystal has been selected and
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the ESW_P3_LED_0 pin is high during reset,
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or a 20MHz crystal has been selected and
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the ESW_P4_LED_0 pin is high during reset,
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then the value of HT_XTAL_FSEL will indicate
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that a 25MHz crystal is present.
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By default, the state of the LED pins is PHY controlled
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to reflect the link state.
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To illustrate, if a board has:
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5 ports with active low LED control,
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and HT_XTAL_FSEL bootstrapped for 40MHz.
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When the MT7530 is powered up without any external
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connection, only the LED associated with Port 3 is
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illuminated as ESW_P3_LED_0 is low.
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In this state, directly after mt7530_setup()'s reset
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is performed, the HWTRAP register (0x7800) reflects
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the intended HT_XTAL_FSEL (HWTRAP bits 10:9) of 40MHz:
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mt7530-mdio mdio-bus:1f: mt7530_read: 00007800 == 00007dcf
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>>> bin(0x7dcf >> 9 & 0b11)
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'0b10'
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But if a cable is connected to Port 3 and the link
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is active before mt7530_setup()'s reset takes place,
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then HT_XTAL_FSEL seems to be set for 25MHz:
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mt7530-mdio mdio-bus:1f: mt7530_read: 00007800 == 00007fcf
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>>> bin(0x7fcf >> 9 & 0b11)
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'0b11'
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Once HT_XTAL_FSEL reflects 25MHz, none of the ports
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are functional until the MT7621 (or MT7530 itself)
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is reset.
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By disabling the LED pins just before reset, the chance
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of an unintended HT_XTAL_FSEL value is reduced.
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Signed-off-by: Justin Swartz <justin.swartz@risingedge.co.za>
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Link: https://lore.kernel.org/r/20240305043952.21590-1-justin.swartz@risingedge.co.za
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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---
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drivers/net/dsa/mt7530.c | 6 ++++++
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1 file changed, 6 insertions(+)
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--- a/drivers/net/dsa/mt7530.c
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+++ b/drivers/net/dsa/mt7530.c
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@@ -2391,6 +2391,12 @@ mt7530_setup(struct dsa_switch *ds)
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}
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}
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+ /* Disable LEDs before reset to prevent the MT7530 sampling a
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+ * potentially incorrect HT_XTAL_FSEL value.
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+ */
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+ mt7530_write(priv, MT7530_LED_EN, 0);
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+ usleep_range(1000, 1100);
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+
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/* Reset whole chip through gpio pin or memory-mapped registers for
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* different type of hardware
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*/
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