linux-kernel - Re: [PATCH 07/11 v5] coresight-etm: add CoreSight ETM/PTM driver

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Date:	Thu, 4 Sep 2014 19:31:02 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Will Deacon <will.deacon@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...aro.org>,
	John Stultz <john.stultz@...aro.org>,
	Pratik Patel <pratikp@...eaurora.org>,
	Vikas Varshney <varshney@...com>, Al Grant <Al.Grant@....com>,
	Jonas Svennebring <jonas.svennebring@...gotech.com>,
	James King <james.king@...aro.org>,
	Panchaxari Prasannamurthy Tumkur 
	<panchaxari.prasannamurthy@...aro.org>,
	Kaixu Xia <kaixu.xia@...aro.org>,
	Marcin Jabrzyk <marcin.jabrzyk@...il.com>,
	"r.sengupta@...sung.com" <r.sengupta@...sung.com>,
	Robert Marklund <robbelibobban@...il.com>,
	Tony Armitstead <Tony.Armitstead@....com>,
	Patch Tracking <patches@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/11 v5] coresight-etm: add CoreSight ETM/PTM driver

On Thu, Sep 4, 2014 at 7:19 PM, Mathieu Poirier
<mathieu.poirier@...aro.org> wrote:
> [Me]:
>> I would rewrite the last function like this:
>>
>> static inline unsigned int etm_readl(struct etm_drvdata *drvdata, u32 off)
>> {
>>        u32 val;
>>
>>        if (drvdata->use_cp14)
>>                asm_volatile()...
>>        else
>>                val = readl_relaxed(drvdata->base + off);
>>        return val;
>> }
>
> That unfortunately won't work.  "u32 off" is a numerical value and it
> works well in the case were CP14 accesses aren't needed.  On the flip
> side that numerical value isn't sufficient to deduce all 3 arguments
> (crn, crm, op2) required by instructions mcr/mrc for the right access
> to happen - there is simply no correlation between the offset of an
> APB bus memory mapped address and the corresponding CP14 access.

You're right, I oversimplified it in my head grossly...

Jens Wiklander pointed me to the macros used in OP-TEE for CP15
access with the same unpredictable patterns:
https://github.com/OP-TEE/optee_os/tree/master/core/arch/arm32/include

Yours,
Linus Walleij
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