Hi Mathieu,
On 2020-04-15 21:26, Mathieu Poirier wrote:
On Tue, 14 Apr 2020 at 09:47, Sai Prakash Ranjan
<saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
Hi Mathieu,
On 2020-04-13 22:44, Mathieu Poirier wrote:
> On Mon, Apr 13, 2020 at 01:55:30PM +0530, Sai Prakash Ranjan wrote:
>> Hi Suzuki,
>>
>> On 2020-04-13 04:47, Suzuki K Poulose wrote:
>> > Hi Sai,
>> >
>> > On 04/09/2020 12:35 PM, Sai Prakash Ranjan wrote:
>> > > Reading TMC mode register in tmc_read_prepare_etb without
>> > > enabling the TMC hardware leads to async exceptions like
>> > > the one in the call trace below. This can happen if the
>> > > user tries to read the TMC etf data via device node without
>> > > setting up source and the sink first which enables the TMC
>> > > hardware in the path. So make sure that the TMC is enabled
>> > > before we try to read TMC data.
>> >
>> > So, one can trigger the same SError by simply :
>> >
>> > $ cat /sys/bus/coresight/device/tmc_etb0/mgmt/mode
>> >
>>
>> I do not see any SError when I run the above command.
>>
>> localhost ~ # cat /sys/bus/coresight/devices/tmc_etf0/mgmt/mode
>> 0x0
>>
>> And this is most likely due to
>>
>> commit cd9e3474bb793dc ("coresight: add PM runtime calls to
>> coresight_simple_func()")
>
> Ok, so this is related to power management (you can ignore my question
> in the
> previous email).
>
> Regarding function tmc_read_prepare_etb(), the best way to deal with
> this is
> probably make sure drvdata->mode != CS_MODE_DISABLED before reading
> TMC_MODE.
> If there is a buffer to read it will have been copied when the ETB was
> disabled
> and there won't be a need to access the HW.
>
This works as well, thanks.
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c
b/drivers/hwtracing/coresight/coresight-tmc-etf.c
index d0cc3985b72a..7ffe05930984 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -596,6 +596,11 @@ int tmc_read_prepare_etb(struct tmc_drvdata
*drvdata)
goto out;
}
+ if (drvdata->mode == CS_MODE_DISABLED) {
+ ret = -EINVAL;
+ goto out;
+ }
+
We are back to your original solution where the ETB buffer can't be
read if the ETB itself is not enabled. It _is_ possible to read the
buffer of an ETB that has been disabled.
To fix this consider the following [1]. Take the block at line 607
and move it to line 598. As part of the if() condition at line 619,
read the value of the TMC_MODE register and exit if not in circular
mode. If it is in circular mode continue with disabling the hardware.
[1].
https://elixir.bootlin.com/linux/v5.7-rc1/source/drivers/hwtracing/coresight/coresight-tmc-etf.c
Thanks, got it now. Posted v2 -
https://lore.kernel.org/patchwork/patch/1226022/
-Sai
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