linux-kernel - Re: [PATCH 07/17] coresight: tmc etr: Add transparent buffer management

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Message-ID: <cc094fc0-3d48-c17f-9afc-25b0a1186dd0@arm.com>
Date:   Fri, 3 Nov 2017 10:02:44 +0000
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        rob.walker@....com, mike.leach@...aro.org,
        coresight@...ts.linaro.org
Subject: Re: [PATCH 07/17] coresight: tmc etr: Add transparent buffer
 management

On 02/11/17 17:48, Mathieu Poirier wrote:
> On Thu, Oct 19, 2017 at 06:15:43PM +0100, Suzuki K Poulose wrote:
>> At the moment we always use contiguous memory for TMC ETR tracing
>> when used from sysfs. The size of the buffer is fixed at boot time
>> and can only be changed by modifiying the DT. With the introduction
>> of SG support we could support really large buffers in that mode.
>> This patch abstracts the buffer used for ETR to switch between a
>> contiguous buffer or a SG table depending on the availability of
>> the memory.
>>
>> This also enables the sysfs mode to use the ETR in SG mode depending
>> on configured the trace buffer size. Also, since ETR will use the
>> new infrastructure to manage the buffer, we can get rid of some
>> of the members in the tmc_drvdata and clean up the fields a bit.
>>
>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>   drivers/hwtracing/coresight/coresight-tmc-etr.c | 433 +++++++++++++++++++-----
>>   drivers/hwtracing/coresight/coresight-tmc.h     |  60 +++-
>>   2 files changed, 403 insertions(+), 90 deletions(-)
>>
> 
> [..]
>   
>> +
>> +static void tmc_etr_sync_sg_buf(struct etr_buf *etr_buf, u64 rrp, u64 rwp)

>> +	w_offset = tmc_sg_get_data_page_offset(table, rwp);
>> +	if (w_offset < 0) {
>> +		dev_warn(table->dev, "Unable to map RWP %llx to offset\n",
>> +				rwp);
> 
>                  dev_warn(table->dev,
>                           "Unable to map RWP %llx to offset\n", rwq);
> 
> It looks a little better and we respect indentation rules.  Same for r_offset.
> 

>> +static inline int tmc_etr_mode_alloc_buf(int mode,
>> +				  struct tmc_drvdata *drvdata,
>> +				  struct etr_buf *etr_buf, int node,
>> +				  void **pages)
> 
> static inline int
> tmc_etr_mode_alloc_buf(int mode,
>                         struct tmc_drvdata *drvdata,
>                         struct etr_buf *etr_buf, int node,
>                         void **pages)

>> + * tmc_alloc_etr_buf: Allocate a buffer use by ETR.
>> + * @drvdata	: ETR device details.
>> + * @size	: size of the requested buffer.
>> + * @flags	: Required properties of the type of buffer.
>> + * @node	: Node for memory allocations.
>> + * @pages	: An optional list of pages.
>> + */
>> +static struct etr_buf *tmc_alloc_etr_buf(struct tmc_drvdata *drvdata,
>> +					  ssize_t size, int flags,
>> +					  int node, void **pages)
> 
> Please fix indentation.  Also @flags isn't used.
> 

Yep, flags is only used later and can move it to the patch where we use it.

>> +{
>> +	int rc = -ENOMEM;
>> +	bool has_etr_sg, has_iommu;
>> +	struct etr_buf *etr_buf;
>> +
>> +	has_etr_sg = tmc_etr_has_cap(drvdata, TMC_ETR_SG);
>> +	has_iommu = iommu_get_domain_for_dev(drvdata->dev);
>> +
>> +	etr_buf = kzalloc(sizeof(*etr_buf), GFP_KERNEL);
>> +	if (!etr_buf)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	etr_buf->size = size;
>> +
>> +	/*
>> +	 * If we have to use an existing list of pages, we cannot reliably
>> +	 * use a contiguous DMA memory (even if we have an IOMMU). Otherwise,
>> +	 * we use the contiguous DMA memory if :
>> +	 *  a) The ETR cannot use Scatter-Gather.
>> +	 *  b) if not a, we have an IOMMU backup
> 
> Please rework the above sentence.

How about :
	   b) if (a) is not true and we have an IOMMU connected to the ETR.

I will address the other comments on indentation.

Thanks for the detailed look

Cheers
Suzuki