Patch "net: dsa: mt7530: prevent possible incorrect XTAL frequency selection" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    net: dsa: mt7530: prevent possible incorrect XTAL frequency selection

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-dsa-mt7530-prevent-possible-incorrect-xtal-frequ.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4e2b74c07bb227872859c347acff31443da1f8aa
Author: Arınç ÜNAL <arinc.unal@xxxxxxxxxx>
Date:   Thu Mar 14 12:28:35 2024 +0300

    net: dsa: mt7530: prevent possible incorrect XTAL frequency selection
    
    [ Upstream commit f490c492e946d8ffbe65ad4efc66de3c5ede30a4 ]
    
    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
    
    Revert commit 2920dd92b980 ("net: dsa: mt7530: disable LEDs before reset").
    Changing the state of pins via reset assertion is simpler and more
    efficient than doing so by setting the LED controller off.
    
    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@xxxxxxxxxxxxxxxx>
    Signed-off-by: Justin Swartz <justin.swartz@xxxxxxxxxxxxxxxx>
    Signed-off-by: Arınç ÜNAL <arinc.unal@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
index 4056ca4255be7..0fbed76bb9697 100644
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -1581,11 +1581,11 @@ 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);
 	}
 
@@ -1704,11 +1704,11 @@ 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);
 	}
 




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