From: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
To: Mike Leach <mike.leach@linaro.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>,
Mathieu Poirier <mathieu.poirier@linaro.org>,
Stephen Boyd <swboyd@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arm-msm@vger.kernel.org,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Russell King <linux@armlinux.org.uk>
Subject: Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple connections
Date: Tue, 12 May 2020 23:16:29 +0530 [thread overview]
Message-ID: <364049a30dc9d242ec611bf27a16a6c9@codeaurora.org> (raw)
In-Reply-To: <CAJ9a7Vg95tcgMXgQKLAZc=TpV6FnPZ7wdF=Kwbuy7d2kRCjYQw@mail.gmail.com>
Hi Mike,
On 2020-05-12 17:19, Mike Leach wrote:
[...]
>> >>
>> >> Sorry for hurrying up and sending the patch -
>> >> https://lore.kernel.org/patchwork/patch/1239923/.
>> >> I will send v2 based on further feedbacks here or there.
>> >>
>> >>>
>> >>> 1) does this replicator part have a unique ID that differs from the
>> >>> standard ARM designed replicators?
>> >>> If so perhaps link the modification into this. (even if the part no
>> >>> in
>> >>> PIDR0/1 is the same the UCI should be different for a different
>> >>> implementation)
>> >>>
> I have reviewed the replicator driver, and compared to all the other CS
> drivers.
> This driver appears to be the only one that sets hardware values in
> probe() and expects them to remain in place on enable, and uses that
> state for programming decisions later, despite telling the PM
> infrastructure that it is clear to suspend the device.
>
> Now we have a system where the replicator hardware is behaving
> differently under the driver, but is it behaving unreasonably?
Thanks for taking your time to review this. For new replicator behaving
unreasonably, I think the assumption that the context is not lost on
disabling clock is flawed since its implementation defined. Is such
assumption documented in any TRM?
>> >>
>> >> pid=0x2bb909 for both replicators. So part number is same.
>> >> UCI will be different for different implementation(QCOM maybe
>> >> different from ARM),
>> >> but will it be different for different replicators under the same
>> >> impl(i.e., on QCOM).
>> >
>> > May be use PIDR4.DES_2 to match the Implementor and apply the work
>> > around for all QCOM replicators ?
>> >
>> > To me that sounds the best option.
>> >
>>
>
> I agree, if it can be established that the register values that make
> up UCI (pid0-4, devarch, devtype, PID:CLASS==0x9), can correctly
> identify the parts then a flag can be set in the probe() function and
> acted on during the enable() function.
>
So here I have a doubt as to why we need to use UCI because PID =
0x2bb909
and CID = 0xb105900d are same for both replicators, so UCI won't
identify the
different replicators(in same implementation i.e., on QCOM) here.
Am I missing something?
Thats why I think Suzuki suggested to use PIDR4_DES2 and check for QCOM
impl
and add a workaround for all replicators, something like below: (will
need cleaning)
#define PIDR4_DES2 0xFD0
if (FIELD_GET(GENMASK(3, 0), readl_relaxed(drvdata->base + PIDR4_DES2))
== 0x4)
id0val = id1val = 0xff;
... and the rest as you suggested.
>
> This was a design decision made by the original driver writer. A
> normal AMBA device should not lose context due to clock removal (see
> drivers/amba/bus.c), so resetting in probe means this operation is
> done only once, rather than add overhead in the enable() function,and
> later decisions can be made according to the state of the registers
> set.
>
> As you have pointed out, for this replicator implementation the
> context is unfortunately not retained when clocks are removed - so an
> alternative method is required.
>
> perhaps something like:-
>
> probe()
> ...
> if (match_id_non_persistent_state_regs(ID))
> drvdata->check_filter_val_on_enable;
> ....
>
> and a re-write of enable:-
>
> enable()
> ...
> CS_UNLOCK()
> id0val = read(IDFILTER0);
> id1val = read(IDFILTER1);
>
> /* some replicator designs lose context when AMBA clocks are removed -
> check for this */
> if (drvdata->check_filter_val_on_enable && (id0val == id1val == 0x0))
> id0val = id1val = 0xff;
>
> if(id0xal == id1val == 0xff)
> rc = claim_device()
>
> if (!rc)
> switch (outport)
> case 0: id0val = 0x0; break
> case 1: id1va; = 0x0; break;
> default: rc = -EINVAL;
>
> if (!rc)
> write(id0val);
> write(id1val);
> CS_LOCK()
> return rc;
> ....
>
Thanks for this detailed idea for workaround. I will add this once we
know whether we need to use UCI or PIDR4_DES2.
> Given that the access to the enable() function is predicated on a
> reference count per active port, there is also a case for dropping the
> check_filter_val_on_enable flag completely - once one port is active,
> then the device will remain enabled until both ports are inactive.
> This still allows for future development of selective filtering per
> port.
>
> One other point here - there is a case as I mentioned above for moving
> to a stored value model for the driver - as this is the only coresight
> driver that appears to set state in the probe() function rather than
> write all on enable.
> This however would necessitate a more comprehensive re-write.
>
I would defer this to experts as you or suzuki will have more idea
regarding this than me.
Thanks,
Sai
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member
of Code Aurora Forum, hosted by The Linux Foundation
next prev parent reply other threads:[~2020-05-12 17:46 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-26 14:37 [PATCH] coresight: dynamic-replicator: Fix handling of multiple connections Sai Prakash Ranjan
2020-04-27 9:20 ` Suzuki K Poulose
2020-04-27 9:45 ` Mike Leach
2020-04-27 13:53 ` Suzuki K Poulose
2020-04-28 12:23 ` Sai Prakash Ranjan
2020-04-29 11:47 ` Sai Prakash Ranjan
2020-04-29 13:49 ` Suzuki K Poulose
2020-04-29 13:59 ` Sai Prakash Ranjan
2020-04-29 14:27 ` Mike Leach
2020-04-29 14:48 ` Sai Prakash Ranjan
2020-04-29 16:58 ` Mike Leach
2020-04-29 17:11 ` Sai Prakash Ranjan
2020-05-06 7:35 ` Sai Prakash Ranjan
2020-05-08 8:53 ` Sai Prakash Ranjan
2020-05-11 11:14 ` Mike Leach
2020-05-11 14:16 ` Sai Prakash Ranjan
2020-05-11 14:30 ` Suzuki K Poulose
2020-05-11 14:41 ` Sai Prakash Ranjan
2020-05-12 11:49 ` Mike Leach
2020-05-12 17:45 ` Mathieu Poirier
2020-05-12 17:46 ` Sai Prakash Ranjan [this message]
2020-05-12 21:52 ` Mike Leach
2020-05-13 1:49 ` Stephen Boyd
2020-05-13 15:45 ` Sai Prakash Ranjan
2020-05-13 15:33 ` Sai Prakash Ranjan
2020-05-16 10:04 ` Sai Prakash Ranjan
2020-05-19 9:04 ` Sai Prakash Ranjan
2020-05-11 14:34 ` Sai Prakash Ranjan
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