Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple connections

[Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>]

Hi Suzuki, Mike,

On 2020-05-06 13:05, Sai Prakash Ranjan wrote:
[...]

>>>> 
>>> OK - sorry I read your statement saying that replicator1 was 0 after
>>> the reset in probe(), rather than look at the logs.
>>> 
>>> From the logs it is working at the time probe() occurs, but by the
>>> time we come to enable the replicator later, something has reset 
>>> these
>>> registers / hardware outside the control of the replicator driver.
>>> 
>> 
>> Yes, I will try to get some more information from the firmware side if
>> there is anything messing up.
>> 
> 
> This turned out to be a clock/pm issue. To confirm, I just marked clk
> as critical
> so that it won't be gated and I saw the replicator1(swao_replicator) 
> registers
> intact after probe. Also alternatively, I tried to comment out 
> disabling pclk
> to check if there is something wrong in amba pm and this keeps the 
> registers
> intact as well.
> 
> @@ -288,7 +295,7 @@ static int amba_probe(struct device *dev)
>                 pm_runtime_set_suspended(dev);
>                 pm_runtime_put_noidle(dev);
> 
> -               amba_put_disable_pclk(pcdev);
> +               //amba_put_disable_pclk(pcdev);
>                 dev_pm_domain_detach(dev, true);
>         } while (0);
> 

I checked with the debug team and there is a limitation with
the replicator(swao_replicator) in the AOSS group where it
loses the idfilter register context when the clock is disabled.
This is not just in SC7180 SoC but also reported on some latest
upcoming QCOM SoCs as well and will need to be taken care in
order to enable coresight on these chipsets.

Here's what's happening -  After the replicator is initialized,
the clock is disabled in amba_pm_runtime_suspend() as a part of
pm runtime workqueue with the assumption that there will be no
loss of context after the replicator is initialized. But it doesn't
hold good with the replicators with these unfortunate limitation
and the idfilter register context is lost.

[    5.889406] amba_pm_runtime_suspend devname=6b06000.replicator ret=0
[    5.914516] Workqueue: pm pm_runtime_work
[    5.918648] Call trace:
[    5.921185]  dump_backtrace+0x0/0x1d0
[    5.924958]  show_stack+0x2c/0x38
[    5.928382]  dump_stack+0xc0/0x104
[    5.931896]  amba_pm_runtime_suspend+0xd8/0xe0
[    5.936469]  __rpm_callback+0xe0/0x140
[    5.940332]  rpm_callback+0x38/0x98
[    5.943926]  rpm_suspend+0xec/0x618
[    5.947522]  rpm_idle+0x5c/0x3f8
[    5.950851]  pm_runtime_work+0xa8/0xc0
[    5.954718]  process_one_work+0x1f8/0x4c0
[    5.958848]  worker_thread+0x50/0x468
[    5.962623]  kthread+0x12c/0x158
[    5.965957]  ret_from_fork+0x10/0x1c

This is a platform/SoC specific replicator issue, so we can either
introduce some DT property for replicators to identify which replicator
has this limitation, check in replicator_enable() and reset the 
registers
or have something like below diff to check the idfilter registers in
replicator_enable() and then reset with clear comment specifying it’s 
the
hardware limitation on some QCOM SoCs. Please let me know your thoughts 
on
this?

diff --git a/drivers/hwtracing/coresight/coresight-replicator.c 
b/drivers/hwtracing/coresight/coresight-replicator.c
index e7dc1c31d20d..a9c039c944eb 100644
--- a/drivers/hwtracing/coresight/coresight-replicator.c
+++ b/drivers/hwtracing/coresight/coresight-replicator.c
@@ -68,6 +68,17 @@ static int dynamic_replicator_enable(struct 
replicator_drvdata *drvdata,
         int rc = 0;
         u32 reg;

+       /*
+        * On some QCOM SoCs with replicators in Always-On domain, 
disabling
+        * clock will result in replicator losing its context. Currently
+        * as a part of pm_runtime workqueue, amba_pm_runtime_suspend 
disables
+        * clock assuming the context is not lost which is not true for 
cases
+        * with hardware limitations as the above.
+        */
+       if ((readl_relaxed(drvdata->base + REPLICATOR_IDFILTER0) == 0) 
&&
+           (readl_relaxed(drvdata->base + REPLICATOR_IDFILTER1) == 0))
+               dynamic_replicator_reset(drvdata);
+
         switch (outport) {
         case 0:
                 reg = REPLICATOR_IDFILTER0;



Thanks,
Sai

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