linux-kernel - Re: [PATCH V2 13/15] coresight: tmc: implementing TMC-ETF AUX space API

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Message-ID: <571661E9.5000007@arm.com>
Date:	Tue, 19 Apr 2016 17:50:49 +0100
From:	Suzuki K Poulose <Suzuki.Poulose@....com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>
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 V2 13/15] coresight: tmc: implementing TMC-ETF AUX space
 API

On 19/04/16 17:45, Mathieu Poirier wrote:
> On 19 April 2016 at 10:16, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
>> On 12/04/16 18:54, 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>
>>> ---
>>>    drivers/hwtracing/coresight/coresight-tmc-etf.c | 198
>>> ++++++++++++++++++++++++
>>>    drivers/hwtracing/coresight/coresight-tmc.h     |  21 +++
>>>    2 files changed, 219 insertions(+)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c
>>> b/drivers/hwtracing/coresight/coresight-tmc-etf.c
>>> index a440784e3b27..fff175d4020d 100644
>>> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
>>> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
>>> @@ -15,7 +15,9 @@
>>>     * this program.  If not, see <http://www.gnu.org/licenses/>.
>>>     */
>>>
>>> +#include <linux/circ_buf.h>
>>>    #include <linux/coresight.h>
>>> +#include <linux/perf_event.h>
>>>    #include <linux/slab.h>
>>>    #include "coresight-priv.h"
>>>    #include "coresight-tmc.h"
>>> @@ -295,9 +297,205 @@ static void tmc_disable_etf_link(struct
>>> coresight_device *csdev,
>>>          dev_info(drvdata->dev, "TMC disabled\n");
>>>    }
>>>
>>> +static void *tmc_alloc_etf_buffer(struct coresight_device *csdev, int
>>> cpu,
>>> +                                 void **pages, int nr_pages, bool
>>> overwrite)
>>
>>
>>
>>
>>> +
>>> +static void tmc_free_etf_buffer(void *config)
>>> +{
>>
>>
>>> +
>>> +static int tmc_set_etf_buffer(struct coresight_device *csdev,
>>> +                             struct perf_output_handle *handle,
>>> +                             void *sink_config)
>>
>>
>>
>>> +static unsigned long tmc_reset_etf_buffer(struct coresight_device *csdev,
>>> +                                         struct perf_output_handle
>>> *handle,
>>> +                                         void *sink_config, bool *lost)
>>> +{
>>
>>
>>
>>>    /**
>>> + * struct cs_buffer - keep track of a recording session' specifics
>>> + * @cur:       index of the current buffer
>>> + * @nr_pages:  max number of pages granted to us
>>> + * @offset:    offset within the current buffer
>>> + * @data_size: how much we collected in this run
>>> + * @lost:      other than zero if we had a HW buffer wrap around
>>> + * @snapshot:  is this run in snapshot mode
>>> + * @data_pages:        a handle the ring buffer
>>> + */
>>> +struct cs_tmc_buffers {
>>> +       unsigned int            cur;
>>> +       unsigned int            nr_pages;
>>> +       unsigned long           offset;
>>> +       local_t                 data_size;
>>> +       local_t                 lost;
>>> +       bool                    snapshot;
>>> +       void                    **data_pages;
>>> +};
>>
>>
>>
>> All of the above look exactly the same as what we have in etb10.c (as you
>> have mentioned).
>> Is there any chance we could reuse them under a generic name ?
>
> I toyed with the idea many times...
>
> Today the structures are similar and can be used in both drivers but
> it is only a matter for time (probably months) before someone adds new
> functionality on one side that isn't compatible with the other side.
> When that happens we'll get a bloated struct with fields that aren't
> used, depending on where it gets instantiated.  Or the struct will be
> split again, coming back to what we have today.
>

If that happens in future, we know what to do now :)

>>> +                * Make sure the new size is aligned in accordance with
>>> the
>>> +                * requirement explained above.
>>> +                */
>>> +               to_read -= handle->size & mask;
>>
>>
>> Shouldn't this be :
>>
>>                  to_read = handle->size & mask;
>
> You are correct.

This applies to the etb10 code as well. So you might want to fix that as well.

Cheers
Suzuki