linux-kernel - Re: [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU

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Date:   Wed, 3 Jun 2020 19:04:35 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rob Herring <robh@...nel.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Frank Rowand <frowand.list@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Sudeep Holla <sudeep.holla@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [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