target/linux/generic/backport-6.6/790-30-v6.9-net-dsa-mt7530-prevent-possible-incorrect-XTAL-frequ.patch

   1 From b9547109205c5e0a27e5bed568b0fc183fff906b Mon Sep 17 00:00:00 2001
   2 From: =?UTF-8?q?Ar=C4=B1n=C3=A7=20=C3=9CNAL?= <arinc.unal@arinc9.com>
   3 Date: Thu, 14 Mar 2024 12:28:35 +0300
   4 Subject: [PATCH 30/30] net: dsa: mt7530: prevent possible incorrect XTAL
   5  frequency selection
   6 MIME-Version: 1.0
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   9
  10 On MT7530, the HT_XTAL_FSEL field of the HWTRAP register stores a 2-bit
  11 value that represents the frequency of the crystal oscillator connected to
  12 the switch IC. The field is populated by the state of the ESW_P4_LED_0 and
  13 ESW_P4_LED_0 pins, which is done right after reset is deasserted.
  14
  15   ESW_P4_LED_0    ESW_P3_LED_0    Frequency
  16   -----------------------------------------
  17   0               0               Reserved
  18   0               1               20MHz
  19   1               0               40MHz
  20   1               1               25MHz
  21
  22 On MT7531, the XTAL25 bit of the STRAP register stores this. The LAN0LED0
  23 pin is used to populate the bit. 25MHz when the pin is high, 40MHz when
  24 it's low.
  25
  26 These pins are also used with LEDs, therefore, their state can be set to
  27 something other than the bootstrapping configuration. For example, a link
  28 may be established on port 3 before the DSA subdriver takes control of the
  29 switch which would set ESW_P3_LED_0 to high.
  30
  31 Currently on mt7530_setup() and mt7531_setup(), 1000 - 1100 usec delay is
  32 described between reset assertion and deassertion. Some switch ICs in real
  33 life conditions cannot always have these pins set back to the bootstrapping
  34 configuration before reset deassertion in this amount of delay. This causes
  35 wrong crystal frequency to be selected which puts the switch in a
  36 nonfunctional state after reset deassertion.
  37
  38 The tests below are conducted on an MT7530 with a 40MHz crystal oscillator
  39 by Justin Swartz.
  40
  41 With a cable from an active peer connected to port 3 before reset, an
  42 incorrect crystal frequency (0b11 = 25MHz) is selected:
  43
  44                       [1]                  [3]     [5]
  45                       :                    :       :
  46               _____________________________         __________________
  47 ESW_P4_LED_0                               |_______|
  48               _____________________________
  49 ESW_P3_LED_0                               |__________________________
  50
  51                        :                  : :     :
  52                        :                  : [4]...:
  53                        :                  :
  54                        [2]................:
  55
  56 [1] Reset is asserted.
  57 [2] Period of 1000 - 1100 usec.
  58 [3] Reset is deasserted.
  59 [4] Period of 315 usec. HWTRAP register is populated with incorrect
  60     XTAL frequency.
  61 [5] Signals reflect the bootstrapped configuration.
  62
  63 Increase the delay between reset_control_assert() and
  64 reset_control_deassert(), and gpiod_set_value_cansleep(priv->reset, 0) and
  65 gpiod_set_value_cansleep(priv->reset, 1) to 5000 - 5100 usec. This amount
  66 ensures a higher possibility that the switch IC will have these pins back
  67 to the bootstrapping configuration before reset deassertion.
  68
  69 With a cable from an active peer connected to port 3 before reset, the
  70 correct crystal frequency (0b10 = 40MHz) is selected:
  71
  72                       [1]        [2-1]     [3]     [5]
  73                       :          :         :       :
  74               _____________________________         __________________
  75 ESW_P4_LED_0                               |_______|
  76               ___________________           _______
  77 ESW_P3_LED_0                     |_________|       |__________________
  78
  79                        :          :       : :     :
  80                        :          [2-2]...: [4]...:
  81                        [2]................:
  82
  83 [1] Reset is asserted.
  84 [2] Period of 5000 - 5100 usec.
  85 [2-1] ESW_P3_LED_0 goes low.
  86 [2-2] Remaining period of 5000 - 5100 usec.
  87 [3] Reset is deasserted.
  88 [4] Period of 310 usec. HWTRAP register is populated with bootstrapped
  89     XTAL frequency.
  90 [5] Signals reflect the bootstrapped configuration.
  91
  92 ESW_P3_LED_0 low period before reset deassertion:
  93
  94               5000 usec
  95             - 5100 usec
  96     TEST     RESET HOLD
  97        #         (usec)
  98   ---------------------
  99        1           5410
 100        2           5440
 101        3           4375
 102        4           5490
 103        5           5475
 104        6           4335
 105        7           4370
 106        8           5435
 107        9           4205
 108       10           4335
 109       11           3750
 110       12           3170
 111       13           4395
 112       14           4375
 113       15           3515
 114       16           4335
 115       17           4220
 116       18           4175
 117       19           4175
 118       20           4350
 119
 120      Min           3170
 121      Max           5490
 122
 123   Median       4342.500
 124      Avg       4466.500
 125
 126 Revert commit 2920dd92b980 ("net: dsa: mt7530: disable LEDs before reset").
 127 Changing the state of pins via reset assertion is simpler and more
 128 efficient than doing so by setting the LED controller off.
 129
 130 Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
 131 Fixes: c288575f7810 ("net: dsa: mt7530: Add the support of MT7531 switch")
 132 Co-developed-by: Justin Swartz <justin.swartz@risingedge.co.za>
 133 Signed-off-by: Justin Swartz <justin.swartz@risingedge.co.za>
 134 Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
 135 Signed-off-by: David S. Miller <davem@davemloft.net>
 136 ---
 137  drivers/net/dsa/mt7530.c | 6 ------
 138  1 file changed, 6 deletions(-)
 139
 140 --- a/drivers/net/dsa/mt7530.c
 141 +++ b/drivers/net/dsa/mt7530.c
 142 @@ -2389,12 +2389,6 @@ mt7530_setup(struct dsa_switch *ds)
 143                 }
 144         }
 145
 146 -       /* Disable LEDs before reset to prevent the MT7530 sampling a
 147 -        * potentially incorrect HT_XTAL_FSEL value.
 148 -        */
 149 -       mt7530_write(priv, MT7530_LED_EN, 0);
 150 -       usleep_range(1000, 1100);
 151 -
 152         /* Reset whole chip through gpio pin or memory-mapped registers for
 153          * different type of hardware
 154          */