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

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Message-ID: <5a76926a6532d3f91cca169d474ba98e@codeaurora.org>
Date:   Wed, 13 May 2020 21:03:41 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Mike Leach <mike.leach@...aro.org>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple
 connections

Hi Mike,

On 2020-05-13 03:22, Mike Leach wrote:

[...]

> 
> Looking at the AMBA driver there is a comment there that AMBA does not
> lose state when clocks are removed. This is consistent with the AMBA
> protocol spec which states that AMBA slaves can only be accessed /
> read / write on various strobe signals,  or state reset on PRESET
> signal, all timed by the rising edge of the bus clock. state changes
> are not permitted on clock events alone. Given this static nature of
> AMBA slaves then removing the clock should not have any effect.
> 
> The AMBA driver only /drivers/amba/bus.c  gives permission to
> remove/restore the clocks from the devices (pm_suspend pm_resume
> callbacks) - this reduces the power consumption of these devices if
> the clock is not running, but state must be retained.
> 

Thanks for the clarification.

>> >> >>
>> >> >> 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;
>> 
> 
> Please look at the CoreSight components specification 3.0 (ARM IHI
> 0029E) Section B2.1.2 which describes the Unique Component Identifier
> (UCI).
> As mentioned above this consists of a combination of bits from
> multiple registers, including PIDR4.
> 

Ok got it now, thanks for clearing the doubt. I will go ahead with
this method to identify QCOM impl and post a patch.

Thanks,
Sai

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