linux-kernel - Re: [PATCH] stm: the number of masters should be (sw_end

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Date:	Fri, 11 Dec 2015 10:51:09 +0200
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Chunyan Zhang <zhang.chunyan@...aro.org>
Cc:	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH] stm: the number of masters should be (sw_end - sw_start + 1)

Chunyan Zhang <zhang.chunyan@...aro.org> writes:

> On Fri, Dec 11, 2015 at 3:31 PM, Alexander Shishkin
> <alexander.shishkin@...ux.intel.com> wrote:
>> Chunyan Zhang <zhang.chunyan@...aro.org> writes:
>>
>>> sw_end represents the last software master, sw_start is index of the
>>> first master, so the number of software masters should be
>>> sw_end - sw_start + 1.
>>
>> Looks about right, but it needs to be in two separate patches.
>>
>>> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
>>> ---
>>>  drivers/hwtracing/intel_th/sth.c | 2 +-
>>>  drivers/hwtracing/stm/core.c     | 2 +-
>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/hwtracing/intel_th/sth.c b/drivers/hwtracing/intel_th/sth.c
>>> index 56101c3..28917d7 100644
>>> --- a/drivers/hwtracing/intel_th/sth.c
>>> +++ b/drivers/hwtracing/intel_th/sth.c
>>> @@ -173,7 +173,7 @@ static int intel_th_sw_init(struct sth_device *sth)
>>>       sth->stm.sw_start = reg & 0xffff;
>>>       sth->stm.sw_end = reg >> 16;
>>>
>>> -     sth->sw_nmasters = sth->stm.sw_end - sth->stm.sw_start;
>>> +     sth->sw_nmasters = sth->stm.sw_end - sth->stm.sw_start + 1;
>>>       dev_dbg(sth->dev, "sw_start: %x sw_end: %x masters: %x nchannels: %x\n",
>>>               sth->stm.sw_start, sth->stm.sw_end, sth->sw_nmasters,
>>>               sth->stm.sw_nchannels);
>>> diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
>>> index 7f7bdb3..cb676f2 100644
>>> --- a/drivers/hwtracing/stm/core.c
>>> +++ b/drivers/hwtracing/stm/core.c
>>> @@ -632,7 +632,7 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data,
>>>       if (!stm_data->packet || !stm_data->sw_nchannels)
>>>               return -EINVAL;
>>>
>>> -     nmasters = stm_data->sw_end - stm_data->sw_start;
>>> +     nmasters = stm_data->sw_end - stm_data->sw_start + 1;
>>>       stm = kzalloc(sizeof(*stm) + nmasters * sizeof(void *), GFP_KERNEL);
>>
>> Or even offsetof(struct stm_device, masters[stm_data->sw_end]).
>>
>
> This should use 'offsetofend()'.

No, actually, just scratch my previous comment as it was completely
wrong, just fix the off-by-one. If we were to use offsetof(), it should
rather be of masters[nmasters], but all we need is to fix the off-by-one
right now.

Regards,
--
Alex
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