linux-kernel - Re: [PATCH V4 16/18] coresight: tmc: implementing TMC-ETF AUX space API

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Date:	Wed, 27 Apr 2016 11:22:19 -0600
From:	Mathieu Poirier <mathieu.poirier@...aro.org>
To:	Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:	"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 V4 16/18] coresight: tmc: implementing TMC-ETF AUX space API

On 27 April 2016 at 05:21, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
> On 26/04/16 23:10, Mathieu Poirier wrote:
>>
>> This patch implement the AUX area interfaces required to
>> use the TMC (configured as an ETF) from the Perf sub-system.
>>
>> The heuristic is heavily borrowed from the ETB10 implementation.
>>
>> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
>
>
>> +
>> +               /*
>> +                * Make sure the new size is aligned in accordance with
>> the
>> +                * requirement explained above.
>> +                */
>> +               to_read = handle->size & mask;
>> +               /* Move the RAM read pointer up */
>> +               read_ptr = (write_ptr + drvdata->size) - to_read;
>> +               /* Make sure we are still within our limits */
>> +               read_ptr &= ~(drvdata->size - 1);
>
>
> Correct me if I am wrong, I think this will break for ETR configuration
> (used from the following
> patch 17/18). Since, for ETR, RRP/RWP will return the lower 32bit AXI
> address (not the queue offset).
> So the last step would really spoil the read_ptr. We might have to set the
> read_ptr by adding the
> appropriate offset from DBAL0.

That's a very good catch.  It also means we ETR support (17/18) has to
be dropped from this set.  I will do a respin of this patch only.

Thanks,
Mathieu

>
> Suzuki
>
>