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Date:   Mon, 7 Feb 2022 12:02:07 -0700
From:   Mathieu Poirier <mathieu.poirier@linaro.org>
To:     Anshuman Khandual <anshuman.khandual@arm.com>
Cc:     James Clark <james.clark@arm.com>, suzuki.poulose@arm.com,
        coresight@lists.linaro.org, leo.yan@linaro.com,
        mike.leach@linaro.org, Leo Yan <leo.yan@linaro.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 01/15] coresight: Make ETM4x TRCIDR0 register accesses
 consistent with sysreg.h
Message-ID: <20220207190207.GB3355405@p14s>
References: <20220203120604.128396-1-james.clark@arm.com>
 <20220203120604.128396-2-james.clark@arm.com>
 <1b649955-cb45-1283-68cd-c82582cef60c@arm.com>
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On Mon, Feb 07, 2022 at 11:14:50AM +0530, Anshuman Khandual wrote:
> Hi James,
> 
> These are all ETM4X specific changes. Something like this might be cleaner
> and also more compact. Also would suggest to follow the same for subsequent
> patches as well.
> 
> coresight: etm4x: Cleanup TRCIDR0 register accesses
> 
> Consistency with sysreg.h could be mentioned in the commit message itself.
>

I agree with the above two comments.

> On 2/3/22 5:35 PM, James Clark wrote:
> > This is a no-op change for style and consistency and has no effect on the
> > binary produced by gcc-11.
> 
> This patch adds register definitions, helper macros as well. Please expand
> the commit message to add more details. This is too short, for the change
> it creates. BTW why is it necessary to mention GCC version number here.
> 

Here too - I'm not sure adding gcc's version number helps in any way.

> > 
> > Signed-off-by: James Clark <james.clark@arm.com>
> > ---
> >  .../coresight/coresight-etm4x-core.c          | 36 +++++--------------
> >  drivers/hwtracing/coresight/coresight-etm4x.h | 17 +++++++++
> >  drivers/hwtracing/coresight/coresight-priv.h  |  5 +++
> >  3 files changed, 30 insertions(+), 28 deletions(-)
> > 
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > index e2eebd865241..107e81948f76 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > @@ -1091,41 +1091,21 @@ static void etm4_init_arch_data(void *info)
> >  	etmidr0 = etm4x_relaxed_read32(csa, TRCIDR0);
> >  
> >  	/* INSTP0, bits[2:1] P0 tracing support field */
> > -	if (BMVAL(etmidr0, 1, 2) == 0b11)
> > -		drvdata->instrp0 = true;
> > -	else
> > -		drvdata->instrp0 = false;
> > -
> > +	drvdata->instrp0 = !!(REG_VAL(etmidr0, TRCIDR0_INSTP0) == 0b11);
> >  	/* TRCBB, bit[5] Branch broadcast tracing support bit */
> > -	if (BMVAL(etmidr0, 5, 5))
> > -		drvdata->trcbb = true;
> > -	else
> > -		drvdata->trcbb = false;
> > -
> > +	drvdata->trcbb = !!(etmidr0 & TRCIDR0_TRCBB);
> >  	/* TRCCOND, bit[6] Conditional instruction tracing support bit */
> > -	if (BMVAL(etmidr0, 6, 6))
> > -		drvdata->trccond = true;
> > -	else
> > -		drvdata->trccond = false;
> > -
> > +	drvdata->trccond = !!(etmidr0 & TRCIDR0_TRCCOND);
> >  	/* TRCCCI, bit[7] Cycle counting instruction bit */
> > -	if (BMVAL(etmidr0, 7, 7))
> > -		drvdata->trccci = true;
> > -	else
> > -		drvdata->trccci = false;
> > -
> > +	drvdata->trccci = !!(etmidr0 & TRCIDR0_TRCCCI);
> >  	/* RETSTACK, bit[9] Return stack bit */
> > -	if (BMVAL(etmidr0, 9, 9))
> > -		drvdata->retstack = true;
> > -	else
> > -		drvdata->retstack = false;
> > -
> > +	drvdata->retstack = !!(etmidr0 & TRCIDR0_RETSTACK);
> >  	/* NUMEVENT, bits[11:10] Number of events field */
> > -	drvdata->nr_event = BMVAL(etmidr0, 10, 11);
> > +	drvdata->nr_event = REG_VAL(etmidr0, TRCIDR0_NUMEVENT);
> >  	/* QSUPP, bits[16:15] Q element support field */
> > -	drvdata->q_support = BMVAL(etmidr0, 15, 16);
> > +	drvdata->q_support = REG_VAL(etmidr0, TRCIDR0_QSUPP);
> >  	/* TSSIZE, bits[28:24] Global timestamp size field */
> > -	drvdata->ts_size = BMVAL(etmidr0, 24, 28);
> > +	drvdata->ts_size = REG_VAL(etmidr0, TRCIDR0_TSSIZE);
> >  
> >  	/* maximum size of resources */
> >  	etmidr2 = etm4x_relaxed_read32(csa, TRCIDR2);
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> > index 3c4d69b096ca..2bd8ad953b8e 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> > @@ -130,6 +130,23 @@
> >  
> >  #define TRCRSR_TA			BIT(12)
> >  
> > +/*
> > + * Bit positions of registers that are defined above, in the sysreg.h style
> > + * of _MASK, _SHIFT and BIT().
> > + */
> 
> ^^^ not really necessary. Instead the format requirement for below mentioned
> CORESIGHT_REG_VAL() macro might be relevant and should be mentioned.

I'm not sure if you're asking to move the comment further below or remove it
altogether.  In any case more comments is always better than less.

> 
> > +#define TRCIDR0_INSTP0_SHIFT			1
> > +#define TRCIDR0_INSTP0_MASK			GENMASK(1, 0)
> > +#define TRCIDR0_TRCBB				BIT(5)
> > +#define TRCIDR0_TRCCOND				BIT(6)
> > +#define TRCIDR0_TRCCCI				BIT(7)
> > +#define TRCIDR0_RETSTACK			BIT(9)
> > +#define TRCIDR0_NUMEVENT_SHIFT			10
> > +#define TRCIDR0_NUMEVENT_MASK			GENMASK(1, 0)
> > +#define TRCIDR0_QSUPP_SHIFT			15
> > +#define TRCIDR0_QSUPP_MASK			GENMASK(1, 0)
> > +#define TRCIDR0_TSSIZE_SHIFT			24
> > +#define TRCIDR0_TSSIZE_MASK			GENMASK(4, 0)
> > +
> >  /*
> >   * System instructions to access ETM registers.
> >   * See ETMv4.4 spec ARM IHI0064F section 4.3.6 System instructions
> > diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> > index ff1dd2092ac5..1452c6038421 100644
> > --- a/drivers/hwtracing/coresight/coresight-priv.h
> > +++ b/drivers/hwtracing/coresight/coresight-priv.h
> > @@ -36,6 +36,11 @@
> >  
> >  #define TIMEOUT_US		100
> >  #define BMVAL(val, lsb, msb)	((val & GENMASK(msb, lsb)) >> lsb)
> > +/*
> > + * Extract a field from a register where field is #defined in the form
> > + * <register_name>_<field_name>_MASK and <register_name>_<field_name>_SHIFT
> > + */
> 
> Looking at the usage, <register_name> is already embedded in <filed_name>. So
> it requires <field_name>_SHIFT and <field_name>_MASK instead. Unless register
> name should be passed as separate argument (which actually might be better).
> 
> REG_VAL(etmidr0, TRCIDR0_TSSIZE) ----> REG_VAL(etmidr0, TRCIDR0, TSSIZE)

I don't have strong preference, I'm good either way.

> 
> with some restructuring in the comment ..
> 
> /*
>  * Extract a field from a coresight register
>  *
>  * Required fields are defined as macros like the following
>  *  
>  * <register_name>_<field_name>_MASK and <register_name>_<field_name>_SHIFT
>  */
> 
> > +#define REG_VAL(val, field)	((val & (field##_MASK << field##_SHIFT)) >> field##_SHIFT)
> 
> This is too generic to be in a coresight header or it should just be
> named CORESIGHT_REG_VAL() instead, making it more specific for here.
> 
> The build should fail in case any required macro definition is absent.
> I guess no more fortification is required in case macros are missing.
> 
> However CORESIGHT_REG_VAL() is better placed in <coresight-etm4x.h>
> just before all the dependent SHIFT/MASK register field definition
> starts.
> 

Not sure about this...  Someone might want to do the same for etmv3 and in that
case we'll end up moving the macro again.

Thanks,
Mathieu

> >  
> >  #define ETM_MODE_EXCL_KERN	BIT(30)
> >  #define ETM_MODE_EXCL_USER	BIT(31)
> > 
> 
> - Anshuman