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SubjectRe: [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU
On Fri, May 29, 2020 at 09:37:58AM +0530, Viresh Kumar wrote:
> On 28-05-20, 13:20, Rob Herring wrote:
> > Whether Linux
> > requires serializing mailbox accesses is a separate issue. On that side,
> > it seems silly to not allow driving the h/w in the most efficient way
> > possible.
>
> That's exactly what we are trying to say. The hardware allows us to
> write all 32 bits in parallel, without any hardware issues, why
> shouldn't we do that ? The delay (which Sudeep will find out, he is
> facing issues with hardware access because of lockdown right now)

OK, I was able to access the setup today. I couldn't reach a point
where I can do measurements as the system just became unusable with
one physical channel instead of 2 virtual channels as in my patches.

My test was simple. Switch to schedutil and read sensors periodically
via sysfs.

arm-scmi firmware:scmi: message for 1 is not expected!
arm-scmi firmware:scmi: timed out in resp(caller: scmi_sensor_reading_get+0xf4/0x120)
arm-scmi firmware:scmi: timed out in resp(caller: scmi_sensor_reading_get+0xf4/0x120)
arm-scmi firmware:scmi: message for 1 is not expected!
arm-scmi firmware:scmi: timed out in resp(caller: scmi_sensor_reading_get+0xf4/0x120)
arm-scmi firmware:scmi: message for 1 is not expected!

With trace enabled I can see even cpufreq_set timing out. Sample trace
output:

bash-1019 [005] 1149.452340: scmi_xfer_begin: transfer_id=1537 msg_id=7 protocol_id=19 seq=0 poll=1
bash-1019 [005] 1149.452407: scmi_xfer_end: transfer_id=1537 msg_id=7 protocol_id=19 seq=0 status=0
bash-1526 [000] 1149.472553: scmi_xfer_begin: transfer_id=1538 msg_id=6 protocol_id=21 seq=0 poll=0
<idle>-0 [001] 1149.472733: scmi_xfer_begin: transfer_id=1539 msg_id=7 protocol_id=19 seq=1 poll=1
<idle>-0 [001] 1149.472842: scmi_xfer_end: transfer_id=1539 msg_id=7 protocol_id=19 seq=1 status=-110
<idle>-0 [001] 1149.483040: scmi_xfer_begin: transfer_id=1540 msg_id=7 protocol_id=19 seq=1 poll=1
<idle>-0 [001] 1149.483043: scmi_xfer_end: transfer_id=1540 msg_id=7 protocol_id=19 seq=1 status=0
rs:main-543 [003] 1149.493031: scmi_xfer_begin: transfer_id=1541 msg_id=7 protocol_id=19 seq=1 poll=1
rs:main-543 [003] 1149.493047: scmi_xfer_end: transfer_id=1541 msg_id=7 protocol_id=19 seq=1 status=0
<idle>-0 [000] 1149.507033: scmi_xfer_begin: transfer_id=1542 msg_id=7 protocol_id=19 seq=1 poll=1
<idle>-0 [000] 1149.507044: scmi_xfer_end: transfer_id=1542 msg_id=7 protocol_id=19 seq=1 status=0
bash-1526 [000] 1149.516068: scmi_xfer_end: transfer_id=1538 msg_id=6 protocol_id=21 seq=0 status=-110
bash-1526 [000] 1149.516559: scmi_xfer_begin: transfer_id=1543 msg_id=6 protocol_id=21 seq=0 poll=0
<idle>-0 [001] 1149.516729: scmi_xfer_begin: transfer_id=1544 msg_id=7 protocol_id=19 seq=1 poll=1
<idle>-0 [001] 1149.516837: scmi_xfer_end: transfer_id=1544 msg_id=7 protocol_id=19 seq=1 status=-110
ksoftirqd/0-9 [000] 1149.519065: scmi_xfer_begin: transfer_id=1545 msg_id=7 protocol_id=19 seq=1 poll=1
ksoftirqd/0-9 [000] 1149.519072: scmi_xfer_end: transfer_id=1545 msg_id=7 protocol_id=19 seq=1 status=0
<idle>-0 [001] 1149.526878: scmi_xfer_begin: transfer_id=1546 msg_id=7 protocol_id=19 seq=1 poll=1
<idle>-0 [001] 1149.526882: scmi_xfer_end: transfer_id=1546 msg_id=7 protocol_id=19 seq=1 status=0
<idle>-0 [000] 1149.551119: scmi_xfer_begin: transfer_id=1547 msg_id=7 protocol_id=19 seq=1 poll=1
<idle>-0 [000] 1149.551138: scmi_xfer_end: transfer_id=1547 msg_id=7 protocol_id=19 seq=1 status=0
bash-1526 [000] 1149.560191: scmi_xfer_end: transfer_id=1543 msg_id=6 protocol_id=21 seq=0 status=-110
bash-1526 [000] 1149.560690: scmi_xfer_begin: transfer_id=1548 msg_id=6 protocol_id=21 seq=0 poll=0
<idle>-0 [001] 1149.560859: scmi_xfer_begin: transfer_id=1549 msg_id=7 protocol_id=19 seq=1 poll=1
<idle>-0 [001] 1149.560968: scmi_xfer_end: transfer_id=1549 msg_id=7 protocol_id=19 seq=1 status=-110

protocol_id=19 is cpufreq and 21 is sensor. This is simplest test and
I can easily generate more timeouts starting some stress test with DVFS.

--
Regards,
Sudeep

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