linux-kernel - Re: [PATCH v5 6/9] coresight: add support for CPU debug module

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Message-ID: <89b6c6c7-0da0-6891-312a-c9221851c20a@arm.com>
Date:   Wed, 29 Mar 2017 11:31:03 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Jonathan Corbet <corbet@....net>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Wei Xu <xuwei5@...ilicon.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Guodong Xu <guodong.xu@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-clk@...r.kernel.org, mike.leach@...aro.org,
        sudeep.holla@....com
Subject: Re: [PATCH v5 6/9] coresight: add support for CPU debug module

On 29/03/17 11:27, Leo Yan wrote:
> On Wed, Mar 29, 2017 at 10:07:07AM +0100, Suzuki K Poulose wrote:
>
> [...]
>
>>>>> +	if (mode == EDDEVID_IMPL_NONE) {
>>>>> +		drvdata->edpcsr_present  = false;
>>>>> +		drvdata->edcidsr_present = false;
>>>>> +		drvdata->edvidsr_present = false;
>>>>> +	} else if (mode == EDDEVID_IMPL_EDPCSR) {
>>>>> +		drvdata->edpcsr_present  = true;
>>>>> +		drvdata->edcidsr_present = false;
>>>>> +		drvdata->edvidsr_present = false;
>>>>> +	} else if (mode == EDDEVID_IMPL_EDPCSR_EDCIDSR) {
>>>>> +		if (!IS_ENABLED(CONFIG_64BIT) &&
>>>>> +			(pcsr_offset == EDDEVID1_PCSR_NO_OFFSET_DIS_AARCH32))
>>>>> +			drvdata->edpcsr_present = false;
>>>>> +		else
>>>>> +			drvdata->edpcsr_present = true;
>>>>
>>>> Sorry, I forgot why we do this check only in this mode. Shouldn't this be
>>>> common to all modes (of course which implies PCSR is present) ?
>>>
>>> No. PCSROffset is defined differently in ARMv7 and ARMv8; So finally we
>>> simplize PCSROffset value :
>>> 0000 - Sample offset applies based on the instruction state (indicated by PCSR[0])
>>> 0001 - No offset applies.
>>> 0010 - No offset applies, but do not use in AArch32 mode!
>>>
>>> So we need handle the corner case is when CPU runs AArch32 mode and
>>> PCSRoffset = 'b0010. Other cases the pcsr should be present.
>>
>> I understand that reasoning. But my question is, why do we check for PCSROffset
>> only when mode == EDDEVID_IMPL_EDPCSR_EDCIDSR and not for say mode == EDDEVID_IMPL_EDPCSR or
>> any other mode where PCSR is present.
>
> Sorry I misunderstood your question.
>
> I made mistake when I analyzed the possbile combination for mode and
> PCSROffset so I thought it's the only case should handle:
> { EDDEVID_IMPL_EDPCSR_EDCIDSR, EDDEVID1_PCSR_NO_OFFSET_DIS_AARCH32 }
>
> Below three combinations are possible to exist; so you are right, I
> should move this out for the checking:
> { EDDEVID_IMPL_NONE,           EDDEVID1_PCSR_NO_OFFSET_DIS_AARCH32 }

That need not be covered, as IMPL_NONE says PCSR is not implemented hence you
don't worry about anything as the functionality is missing. This should rather be:
EDDEVID_IMPL_EDPCSR, where only PCSR is implemented.

My switch...case suggestion makes it easier to do all this checking.


Thanks
Suzuki