Re: [PATCH] net: dsa: mt7530: disable LEDs before reset
From: Justin Swartz
Date: Tue Mar 12 2024 - 08:08:18 EST
Arınç
On 2024-03-12 04:41, Arınç ÜNAL wrote:
On 12.03.2024 03:07, Justin Swartz wrote:
I took a similar approach, with calls to dev_info()
throughout mt7530_setup() plus mt7530_write(), mt7530_read()
and mt7530_rmw() to get an idea of the flow of execution and
which registers were being manipulated.
Calls to dev_info() affected timing, so I switched to using
trace_printk() and then read the output from the debugfs's
tracing/trace file instead of from the console.
I attached a logic analyzer to ESW_P4_LED_0 and ESW_P3_LED_0,
and manually triggered sampling as soon as execution of the
kernel was reported on UART1.
-- Test #1 -----------------------------------------------------------
For the sake of maximal reproducability, I removed the delay
between the assertion and deassertion of reset and added
HWTRAP value tracing:
---%---
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -2243,7 +2243,6 @@ mt7530_setup(struct dsa_switch *ds)
*/
if (priv->mcm) {
reset_control_assert(priv->rstc);
- usleep_range(1000, 1100);
reset_control_deassert(priv->rstc);
} else {
gpiod_set_value_cansleep(priv->reset, 0);
@@ -2260,6 +2259,10 @@ mt7530_setup(struct dsa_switch *ds)
return ret;
}
+ static char ht_xtal_fsel[4][6] = { "?????", "20MHz", "40MHz",
"25MHz" };
+ trace_printk("HWTRAP = %x, HT_XTAL_FSEL = %s\n",
+ val, ht_xtal_fsel[(val & HWTRAP_XTAL_MASK) >> 9]);
+
id = mt7530_read(priv, MT7530_CREV);
id >>= CHIP_NAME_SHIFT;
if (id != MT7530_ID) {
---%---
(a) Without a cable connected to Port 3 (lan4) before reset, the
correct external crystal frequency is selected:
[3] [4] [6]
: : :
_________
______________________________________
ESW_P4_LED_0 |_______|
_______
ESW_P3_LED_0 _________| |______________________________________
: :
[5]...:
[3] Port 4 LED Off. Port 3 LED On.
[4] Signals inverted. (reset_control_assert; reset_control_deassert)
[5] Period of 310 usec.
[6] Signals reflect the bootstrapped configuration.
~ # sed -n -e '$s/^.*\. //p' /sys/kernel/debug/tracing/trace
2.432646: mt7530_setup: HWTRAP = 7dcf, HT_XTAL_FSEL = 40MHz
(b) When a cable attached to an active peer is connected to
Port 3 (lan4) before reset, the incorrect crystal frequency
selection (0b11 = 25MHz) always occurs:
[7] [8] [10] [12]
: : : :
_________
______________________________________
ESW_P4_LED_0 |_______|
_________ _______
ESW_P3_LED_0 |_______| |______________________________
: : : :
[9]...: [11]..:
[7] Port 4 LED Off. Port 3 LED Off.
[8] Signals inverted. (reset_control_assert; reset_control_deassert)
[9] Period of 320 usec.
[10] Signals inverted.
[11] Period of 300 usec.
[12] Signals reflect the bootstrapped configuration.
~ # sed -n -e '$s/^.*\. //p' /sys/kernel/debug/tracing/trace
2.432884: mt7530_setup: HWTRAP = 7fcf, HT_XTAL_FSEL = 25MHz
-- Test #2 -----------------------------------------------------------
To attempt to determine which transitions are associated
with asserting and deasserting reset, I performed another
test with a delay of what I intended to be a 1 sec period
where the MT7530 is held in reset:
---%---
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -2243,7 +2243,7 @@ mt7530_setup(struct dsa_switch *ds)
*/
if (priv->mcm) {
reset_control_assert(priv->rstc);
- usleep_range(1000, 1100);
+ usleep_range(1000000, 1000000);
reset_control_deassert(priv->rstc);
} else {
gpiod_set_value_cansleep(priv->reset, 0);
@@ -2260,6 +2260,10 @@ mt7530_setup(struct dsa_switch *ds)
return ret;
}
+ static char ht_xtal_fsel[4][6] = { "?????", "20MHz", "40MHz",
"25MHz" };
+ trace_printk("HWTRAP = %x, HT_XTAL_FSEL = %s\n",
+ val, ht_xtal_fsel[(val & HWTRAP_XTAL_MASK) >> 9]);
+
id = mt7530_read(priv, MT7530_CREV);
id >>= CHIP_NAME_SHIFT;
if (id != MT7530_ID) {
---%---
(a) Without a cable connected to Port 3 (lan4) before reset, the
correct external crystal frequency is again selected:
[13] [14] [16]
: : :
_________
______________________________________
ESW_P4_LED_0 |_______|
_______
ESW_P3_LED_0 _________| |______________________________________
: :
[15]..:
[13] Port 4 LED Off. Port 3 LED On.
[14] Signals inverted. (reset_control_deassert?)
[15] Period of 310 usec.
[16] Signals reflect the bootstrapped configuration.
~ # sed -n -e '$s/^.*\. //p' /sys/kernel/debug/tracing/trace
3.437461: mt7530_setup: HWTRAP = 7dcf, HT_XTAL_FSEL = 40MHz
No difference is apparent in the timing diagram, compared
to the result from Test #1a, but it is obvious that the code
which follows the reset was executed about 1 second later.
(b) With a cable from an active peer connected to Port 3
(lan4) before reset, the correct crystal frequency
(0b10 = 40MHz) is selected:
[17] [18] [20] [22]
: : : :
______________________ \ \ ______
_______________
ESW_P4_LED_0 / / |______|
_________ \ \ ______
ESW_P3_LED_0 |____________ / / ______| |_______________
\ \
: : : :
[19]..................: [21].:
[17] Port 4 LED Off. Port 3 LED Off.
[18] ESW_P3_LED_0 set low. (reset_control_assert?)
[19] Period of 1000.325 msec.
[20] Signals inverted. (reset_control_deassert?)
[21] Period of 310 usec.
[22] Signals reflect the bootstrapped configuration.
~ # sed -n -e '$s/^.*\. //p' /sys/kernel/debug/tracing/trace
3.433235: mt7530_setup: HWTRAP = 7dcf, HT_XTAL_FSEL = 40MHz
So it appears that when reset is deasserted, the ESW_P4_LED_0
and ESW_P3_LED_0 levels are inverted for a period of about
300 - 310 usec in Test #1a, #1b, #2a, and #2b.
Co-incidentally, these inverted levels are the active low
representation of what ends up in HT_XTAL_FSEL. And in all
four examples, have been the inversion of what immediately
preceded reset_control_deassert().
-- Test #3 -----------------------------------------------------------
Now it seems that there is a signature that can be used
to identify when reset_control_deassert() is executed,
the time of reset_control_assert()'s execution should be
between (at most) 1100 and (at least) 1000 usec prior
based on the unmodified reset logic.
So this patch only includes the HT_XTAL_FSEL trace.
---%---
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -2260,6 +2260,10 @@ mt7530_setup(struct dsa_switch *ds)
return ret;
}
+ static char ht_xtal_fsel[4][6] = { "?????", "20MHz", "40MHz",
"25MHz" };
+ trace_printk("HWTRAP = %x, HT_XTAL_FSEL = %s\n",
+ val, ht_xtal_fsel[(val & HWTRAP_XTAL_MASK) >> 9]);
+
id = mt7530_read(priv, MT7530_CREV);
id >>= CHIP_NAME_SHIFT;
if (id != MT7530_ID) {
---%---
The purpose of the following examples are to show the
variance in how long it takes for ESW_P3_LED_0 to go low.
(a) With a cable from an active peer connected to Port 3
(lan4) before reset, the correct crystal frequency
(0b10 = 40MHz) is selected.
[23] [24] [26] [28] [30]
: : : : :
_____________________________
__________________
ESW_P4_LED_0 |_______|
___________________ _______
ESW_P3_LED_0 |_________| |__________________
: : : : :
: [27]....: [29]..:
[25]...............:
[23] Port 4 LED Off. Port 3 LED Off.
[24] Approximate point of reset_control_assert?
[25] Period of approximately 1000 - 1100 usec.
[26] ESW_P3_LED_0 finally goes low.
[27] Period of 415 usec.
[28] Signals inverted. (reset_control_deassert?)
[29] Period of 310 usec.
[30] Signals reflect the bootstrapped configuration.
(b) With a cable from an active peer connected to Port 3
(lan4) before reset, the correct crystal frequency
(0b10 = 40MHz) is selected.
[31] [32] [34] [36] [38]
: : : : :
_____________________________
__________________
ESW_P4_LED_0 |_______|
___________________________ _______
ESW_P3_LED_0 |_| |__________________
: : : :
: [35] [37]..:
: :
[33]...............:
[31] Port 4 LED Off. Port 3 LED Off.
[32] Approximate point of reset_control_assert?
[33] Period of approximately 1000 - 1100 usec.
[34] ESW_P3_LED_0 finally goes low.
[35] Period of 50 usec.
[36] Signals inverted. (reset_control_deassert?)
[37] Period of 310 usec.
[38] Signals reflect the bootstrapped configuration.
(c) With a cable from an active peer connected to Port 3
(lan4) before reset, an incorrect crystal frequency
(0b11 = 25MHz) is selected.
[45] [46] [48] [50]
: : : :
_____________________________
__________________
ESW_P4_LED_0 |_______|
_____________________________
ESW_P3_LED_0 |__________________________
: : : :
: : [49]..:
: :
[47]...............:
[45] Port 4 LED Off. Port 3 LED Off.
[46] Approximate point of reset_control_assert?
[47] Period of approximately 1000 - 1100 usec.
[48] Signals inverted. (reset_control_deassert?)
[49] Period of 315 usec.
[50] Signals reflect the bootstrapped configuration.
~ # sed -n -e '$s/^.*\. //p' /sys/kernel/debug/tracing/trace
2.617819: mt7530_setup: HWTRAP = 7fcf, HT_XTAL_FSEL = 25MHz
~ # cat /proc/cmdline
console=ttyS0,57600 loglevel=7 printk.time=1 root=/dev/ram0 debug
rdinit=/linuxrc
-- End of Tests ------------------------------------------------------
It seems that the incorrect crystal frequency is selected more
often when debugging messages are present (such as printk()
based approaches) and especially when loglevel=7 and printk.time=1
are specified on the command line.
For the sake of reference: I disabled ethernet support in my build
of (mainline) U-boot, and my kernel configuration is a very lean
selection of options suited for IP routing and a few peripherals
on the I2C and SPI buses.
My userland is confined to an initramfs built around busybox.
I also disable gmac1 because I need a few of the rgmii2 pins for
modem control signalling.
Regards
Justin
PS: Yes, I only have access to MT7621AT SoCs.
Thanks for the detailed presentation. I've simplified it to this, from
what
I understood.
--- Currently
-------------------------------------------------------------
With a cable from an active peer connected to Port 3 (lan4) before
reset:
Test 1, 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_control_assert.
[2] Period of 1000 - 1100 usec.
[2-1] ESW_P3_LED_0 goes low.
[2-2] Period of 415 usec.
[3] reset_control_deassert.
[4] Period of 310 usec. HWTRAP register is populated with bootstrapped
XTAL frequency.
[5] Signals reflect the bootstrapped configuration.
Test 2, an incorrect crystal frequency (0b11 = 25MHz) is selected.
[2] [4] [6]
: : :
_____________________________ __________________
ESW_P4_LED_0 |_______|
_____________________________
ESW_P3_LED_0 |__________________________
: : : :
: : [5]...:
: :
[3]................:
[1] reset_control_assert.
[2] Period of 1000 - 1100 usec.
[3] reset_control_deassert.
[5] Period of 315 usec. HWTRAP register is populated with incorrect
XTAL frequency.
[6] Signals reflect the bootstrapped configuration.
--- 1 second delay between assert and deassert
----------------------------
With a cable from an active peer connected to Port 3 (lan4) 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_control_assert.
[3] Period of 1000.325 msec.
[2-1] ESW_P3_LED_0 goes low.
[2-2] Remaining period of 1000.325 msec.
[3] reset_control_deassert.
[4] Period of 310 usec. HWTRAP register is populated with bootstrapped
XTAL frequency.
[5] Signals reflect the bootstrapped configuration.
---
Wouldn't it be a better idea to 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) instead of disabling the LED
controller and delaying before reset?
I've done some additional tests to see what the difference would be
between increasing the reset hold period vs. disabling the LEDs then
sleeping before reset.
I wanted to know:
When an active link is present on Port 3 at boot, what are the
minimum, maximum and average periods between ESW_P3_LED_0
going low and the signal inversion that seems to co-incide with
reset_control_deassert() for each approach?
I created two patches:
WITH INCREASED RESET DELAY
As I submitted a patch that added an intended 1000 - 1100 usec delay
before reset, I thought it would be fair to increase the reset hold
period by the same value.
---%---
--- 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(2000, 2200);
reset_control_deassert(priv->rstc);
} else {
gpiod_set_value_cansleep(priv->reset, 0);
- usleep_range(1000, 1100);
+ usleep_range(2000, 2200);
gpiod_set_value_cansleep(priv->reset, 1);
}
---%---
DISABLE LEDS BEFORE RESET
Reset hold period unchanged from the intended 1000 - 1100 usec.
---%---
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -2238,6 +2238,12 @@ mt7530_setup(struct dsa_switch *ds)
}
}
+ /* Disable LEDs before reset to prevent the MT7530 sampling a
+ * potentially incorrect HT_XTAL_FSEL value.
+ */
+ mt7530_write(priv, MT7530_LED_EN, 0);
+ usleep_range(1000, 1100);
+
/* Reset whole chip through gpio pin or memory-mapped registers
for
* different type of hardware
*/
---%---
I ran 20 tests per patch, applied exclusively. 40 tests in total.
<-- ESW_P3_LED_0 Low Period before Reset Deassertion -->
TEST WITH INCREASED RESET DELAY DISABLE LEDS BEFORE RESET
# (usec) (usec)
-------------------------------------------------------------------
1 182 4790
2 370 3470
3 240 4635
4 1475 4850
5 70 4775
6 2730 4575
7 3180 4565
8 265 5650
9 270 4690
10 1525 4450
11 3210 4735
12 120 4690
13 185 4625
14 305 7020
15 2975 4720
16 245 4675
17 350 4740
18 80 17920
19 150 17665
20 100 4620
Min 70 3470
Max 3210 17920
Mean 270 4720
Avg 923.421 6161.579
Every test resulted in a 40MHz HT_XTAL_FSEL, but after seeing 70 usec
and 80 usec periods I wondered how many more tests it may take before
an 25MHz HT_XTAL_FSEL appears.
I was also surprised by the 17920 usec and 17665 usec periods listed
under the DISABLED LEDS BEFORE RESET column. Nothing unusual seemed
to be happening, at least as far as the kernel message output was
concerned.
What do you make of these results?
One MT7531 pin used for an LED is also used to decide the crystal
frequency
between 40MHz and 25Mhz. We should implement this there as well.
Arınç