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

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Date:	Fri, 11 Dec 2015 17:10:36 +0800
From:	Chunyan Zhang <zhang.chunyan@...aro.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	"linux-kernel@...r.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)

On Fri, Dec 11, 2015 at 4:51 PM, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> 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.
>

Sorry, you may lose me here, what's 'off-by-one' ?

Thanks,
Chunyan

> Regards,
> --
> Alex
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