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

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Date:   Thu, 13 Jan 2022 20:31:19 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     "Martinez, Ricardo" <ricardo.martinez@...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 Wed, 12 Jan 2022, Martinez, Ricardo wrote:

> 
> 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?

I think list_is_last() is fine if that's what you want to use.
...I missed earlier the fact that you were referring to something else 
than list_entry_is_last thanks to these n similarly named functions :-).

-- 
 i.