[PATCH -next v2] wifi: mac80211: use max to simplify the code

[PATCH -next v2] wifi: mac80211: use max to simplify the code

[Hongbo Li]

The following Coccinelle/coccicheck warning reported by
minmax.cocci:
    WARNING opportunity for max()
Let's use max() to simplify the code and fix the warning.

Signed-off-by: Hongbo Li <lihongbo22@huawei.com>

---
v2:
  - change the commit title

v1: https://patchwork.kernel.org/project/linux-wireless/patch/20240824074033.2134514-2-lihongbo22@huawei.com/
---
 net/mac80211/driver-ops.h | 2 +-
 net/mac80211/mlme.c       | 2 +-
 net/mac80211/scan.c       | 6 ++----
 net/mac80211/tdls.c       | 2 +-
 4 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/mac80211/driver-ops.h b/net/mac80211/driver-ops.h
index d382d9729e85..6b75c7eeff25 100644
--- a/net/mac80211/driver-ops.h
+++ b/net/mac80211/driver-ops.h
@@ -971,7 +971,7 @@ drv_mgd_protect_tdls_discover(struct ieee80211_local *local,
 		return;
 	WARN_ON_ONCE(sdata->vif.type != NL80211_IFTYPE_STATION);
 
-	link_id = link_id > 0 ? link_id : 0;
+	link_id = max(link_id, 0);
 
 	trace_drv_mgd_protect_tdls_discover(local, sdata);
 	if (local->ops->mgd_protect_tdls_discover)
diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 4779a18ab75d..60a7631f0457 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -5375,7 +5375,7 @@ ieee80211_determine_our_sta_mode_auth(struct ieee80211_sub_if_data *sdata,
 				      struct ieee80211_conn_settings *conn)
 {
 	ieee80211_determine_our_sta_mode(sdata, sband, NULL, wmm_used,
-					 req->link_id > 0 ? req->link_id : 0,
+					 max(req->link_id, 0),
 					 conn);
 }
 
diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index b5f2df61c7f6..e77c9f07b046 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -1013,10 +1013,8 @@ static void ieee80211_scan_state_set_channel(struct ieee80211_local *local,
 	 */
 	if ((chan->flags & (IEEE80211_CHAN_NO_IR | IEEE80211_CHAN_RADAR)) ||
 	    !scan_req->n_ssids) {
-		*next_delay = msecs_to_jiffies(scan_req->duration) >
-			      IEEE80211_PASSIVE_CHANNEL_TIME ?
-			      msecs_to_jiffies(scan_req->duration) :
-			      IEEE80211_PASSIVE_CHANNEL_TIME;
+		*next_delay = max(msecs_to_jiffies(scan_req->duration),
+				  IEEE80211_PASSIVE_CHANNEL_TIME);
 		local->next_scan_state = SCAN_DECISION;
 		if (scan_req->n_ssids)
 			set_bit(SCAN_BEACON_WAIT, &local->scanning);
diff --git a/net/mac80211/tdls.c b/net/mac80211/tdls.c
index f07b40916485..719739def96c 100644
--- a/net/mac80211/tdls.c
+++ b/net/mac80211/tdls.c
@@ -919,7 +919,7 @@ ieee80211_tdls_build_mgmt_packet_data(struct ieee80211_sub_if_data *sdata,
 	int ret;
 	struct ieee80211_link_data *link;
 
-	link_id = link_id >= 0 ? link_id : 0;
+	link_id = max(link_id, 0);
 	rcu_read_lock();
 	link = rcu_dereference(sdata->link[link_id]);
 	if (WARN_ON(!link))
-- 
2.34.1

Re: [PATCH -next v2] wifi: mac80211: use max to simplify the code

[Johannes Berg]

On Tue, 2024-08-27 at 11:03 +0800, Hongbo Li wrote:
> The following Coccinelle/coccicheck warning reported by
> minmax.cocci:
>     WARNING opportunity for max()

Yeah well, maybe sometimes we shouldn't blindly follow tools ...

> Let's use max() to simplify the code and fix the warning.

You should explain why.

I think only one out of four changes in this patch is correct,
semantically.

johannes

Re: [PATCH -next v2] wifi: mac80211: use max to simplify the code

[Hongbo Li]

On 2024/8/27 15:25, Johannes Berg wrote:
> On Tue, 2024-08-27 at 11:03 +0800, Hongbo Li wrote:
>> The following Coccinelle/coccicheck warning reported by
>> minmax.cocci:
>>      WARNING opportunity for max()
> 
> Yeah well, maybe sometimes we shouldn't blindly follow tools ...
> 
>> Let's use max() to simplify the code and fix the warning.
> 
> You should explain why.
> 
> I think only one out of four changes in this patch is correct,
> semantically.
> 
You mean sometimes we should keep the variable type in comparison?

Thanks,
Hongbo

> johannes
> 

Re: [PATCH -next v2] wifi: mac80211: use max to simplify the code

[Johannes Berg]

On Tue, 2024-08-27 at 15:29 +0800, Hongbo Li wrote:
> 
> On 2024/8/27 15:25, Johannes Berg wrote:
> > On Tue, 2024-08-27 at 11:03 +0800, Hongbo Li wrote:
> > > The following Coccinelle/coccicheck warning reported by
> > > minmax.cocci:
> > >      WARNING opportunity for max()
> > 
> > Yeah well, maybe sometimes we shouldn't blindly follow tools ...
> > 
> > > Let's use max() to simplify the code and fix the warning.
> > 
> > You should explain why.
> > 
> > I think only one out of four changes in this patch is correct,
> > semantically.
> > 
> You mean sometimes we should keep the variable type in comparison?

No, I just don't think these are semantically calculations of a maximum,
even if they look that way.

That's why I asked: Why are you making this change? It looks like you're
making this change just because you want coccicheck to be silent here.
But that's *really* not a good reason! Don't do that, ever, *think*
about the changes you're making too.

We should consider the primary consumer of the code to be *people*, not
the compiler or tools like coccicheck. And for *people*, applying max()
to a link ID makes no sense. It's a link ID, not any kind of value that
applying max() to makes any sense.
In contrast, for the timeout value there that you changed, that _does_
make sense: it clearly wants to take the longer of the two durations.


So then why do we have patterns that look like max(0, link_id)? That's
because we treat -1 as a special value indicating "no link, but for the
whole sta/vif/...", "don't care about the link" or "MLD not used"
(depending on the context). Internally in the code, however, we use 0
for non-MLD to simplify older drivers and internal logic.

That's why we end up with "link_id >= 0 ? link_id : 0" in some places.
But it's fundamentally not max() even though it looks like it. Replacing
it with max() does this a disservice.

Now arguably open-coding it often (though three perhaps isn't often, but
I'm surprised it's only three times) maybe isn't a great idea either,
but then that should be solved differently.

So yeah, please think about changes, don't make them blindly.

johannes