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

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Date:   Wed, 12 Jan 2022 11:03:06 -0800
From:   "Martinez, Ricardo" <ricardo.martinez@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     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 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()?

This way we avoid accessing head if not needed and does not to use 
'container_of()' on (pos)->member.next.

     (list_is_last(&(pos)->member, head) ? \
     list_first_entry(head, typeof(*(pos)), member) : \
     list_next_entry(pos, member))

(untested)

>>>>>      list_first_entry(ptr, typeof(*(pos)), member) : \
>>>>>      list_next_entry(pos, member))