netdev - Re: [PATCH net-next v3 01/12] net: wwan: t7xx: Add control DMA interface

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Message-ID: <61183e27-e83a-81b2-5f86-cedb39a50382@linux.intel.com>
Date:   Wed, 12 Jan 2022 12:08:25 -0800
From:   "Martinez, Ricardo" <ricardo.martinez@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
        kuba@...nel.org, davem@...emloft.net, johannes@...solutions.net,
        ryazanov.s.a@...il.com, loic.poulain@...aro.org,
        m.chetan.kumar@...el.com, chandrashekar.devegowda@...el.com,
        linuxwwan@...el.com, chiranjeevi.rapolu@...ux.intel.com,
        haijun.liu@...iatek.com, amir.hanania@...el.com,
        dinesh.sharma@...el.com, eliot.lee@...el.com,
        mika.westerberg@...ux.intel.com, moises.veleta@...el.com,
        pierre-louis.bossart@...el.com, muralidharan.sethuraman@...el.com,
        Soumya.Prakash.Mishra@...el.com, sreehari.kancharla@...el.com
Subject: Re: [PATCH net-next v3 01/12] net: wwan: t7xx: Add control DMA
 interface


On 1/12/2022 11:24 AM, Ilpo Järvinen wrote:
> On Wed, 12 Jan 2022, Martinez, Ricardo wrote:
>
>> On 1/12/2022 10:16 AM, Ilpo Järvinen wrote:
>>> On Wed, 12 Jan 2022, Andy Shevchenko wrote:
>>>
>>>> On Wed, Jan 12, 2022 at 04:24:52PM +0200, Ilpo Järvinen wrote:
>>>>> On Wed, 12 Jan 2022, Andy Shevchenko wrote:
>>>>>> On Tue, Jan 11, 2022 at 08:55:58PM -0800, Martinez, Ricardo wrote:
>>>>>>> On 12/16/2021 3:08 AM, Ilpo Järvinen wrote:
>>>>>>>> On Mon, 6 Dec 2021, Ricardo Martinez wrote:
>>>>>>>>> +	if (req->entry.next == &ring->gpd_ring)
>>>>>>>>> +		return list_first_entry(&ring->gpd_ring, struct
>>>>>>>>> cldma_request, entry);
>>>>>>>>> +
>>>>>>>>> +	return list_next_entry(req, entry);
>>>>>> ...
>>>>>>
>>>>>>>>> +	if (req->entry.prev == &ring->gpd_ring)
>>>>>>>>> +		return list_last_entry(&ring->gpd_ring, struct
>>>>>>>>> cldma_request, entry);
>>>>>>>>> +
>>>>>>>>> +	return list_prev_entry(req, entry);
>>>>>> ...
>>>>>>
>>>>>>>> Wouldn't these two seems generic enough to warrant adding
>>>>>>>> something like
>>>>>>>> list_next/prev_entry_circular(...) to list.h?
>>>>>>> Agree, in the upcoming version I'm planning to include something
>>>>>>> like this
>>>>>>> to list.h as suggested:
>>>>>> I think you mean for next and prev, i.o.w. two helpers, correct?
>>>>>>
>>>>>>> #define list_next_entry_circular(pos, ptr, member) \
>>> One thing I missed earlier, the sigrature should instead of ptr have head:
>>> #define list_next_entry_circular(pos, head, member)
>>>
>>>>>>>       ((pos)->member.next == (ptr) ? \
>>>>>> I believe this is list_entry_is_head().
>>>>> It takes .next so it's not the same as list_entry_is_head() and
>>>>> list_entry_is_last() doesn't exist.
>>>> But we have list_last_entry(). So, what about
>>>>
>>>> list_last_entry() == pos ? first : next;
>>>>
>>>> and counterpart
>>>>
>>>> list_first_entry() == pos ? last : prev;
>>>>
>>>> ?
>>> Yes, although now that I think it more, using them implies the head
>>> element has to be always accessed. It might be marginally cache friendlier
>>> to use list_entry_is_head you originally suggested but get the next entry
>>> first:
>>> ({
>>> 	typeof(pos) next__ = list_next_entry(pos, member); \
>>> 	!list_entry_is_head(next__, head, member) ? next__ :
>>> list_next_entry(next__, member);
>>> })
>>> (This was written directly to email, entirely untested).
>>>
>>> Here, the head element would only get accessed when we really need to walk
>>> through it.
>> I'm not sure if list_next_entry() will work for the last element, what about
>> using list_is_last()?
> Why wouldn't it? E.g., list_for_each_entry() does it for the last entry
> before terminating the for loop.

I wasn't sure about using container_of() on the head of the list, but I 
see that it is not a problem.

Would that still be preferred over the list_is_last() approach?