[PATCH] mac80211: allow overriding station bandwidth.

[PATCH] mac80211: allow overriding station bandwidth.

[greearb]

From: Ben Greear <greearb@candelatech.com>

This allows one to disable VHT160 (or 80+80) on hardware
that might otherwise try to use it.  One potential reason
to do this is that at least some 160Mhz/80+80 hardware can
only do 2x2 at 160Mhz, but can do 4x4 at 80Mhz.  And, due to
driver and firmware issues, it may effectively be limitted
to 1x1 at 160Mhz for some NICs.

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
 include/linux/ieee80211.h |  1 +
 net/mac80211/main.c       |  1 +
 net/mac80211/vht.c        | 23 +++++++++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h
index a80516f..e5dc3a8 100644
--- a/include/linux/ieee80211.h
+++ b/include/linux/ieee80211.h
@@ -1542,6 +1542,7 @@ struct ieee80211_vht_operation {
 #define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_160MHZ		0x00000004
 #define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_160_80PLUS80MHZ	0x00000008
 #define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK			0x0000000C
+#define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_SHIFT			2
 #define IEEE80211_VHT_CAP_RXLDPC				0x00000010
 #define IEEE80211_VHT_CAP_SHORT_GI_80				0x00000020
 #define IEEE80211_VHT_CAP_SHORT_GI_160				0x00000040
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index ec5587d..1447b47 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -464,6 +464,7 @@ static const struct ieee80211_ht_cap mac80211_ht_capa_mod_mask = {
 static const struct ieee80211_vht_cap mac80211_vht_capa_mod_mask = {
 	.vht_cap_info =
 		cpu_to_le32(IEEE80211_VHT_CAP_RXLDPC |
+			    IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK |
 			    IEEE80211_VHT_CAP_SHORT_GI_80 |
 			    IEEE80211_VHT_CAP_SHORT_GI_160 |
 			    IEEE80211_VHT_CAP_RXSTBC_1 |
diff --git a/net/mac80211/vht.c b/net/mac80211/vht.c
index 720c64c..5684e13 100644
--- a/net/mac80211/vht.c
+++ b/net/mac80211/vht.c
@@ -56,6 +56,29 @@ void ieee80211_apply_vhtcap_overrides(struct ieee80211_sub_if_data *sdata,
 	__check_vhtcap_disable(sdata, vht_cap,
 			       IEEE80211_VHT_CAP_TX_ANTENNA_PATTERN);
 
+	/* Allow disabling 160Mhz or 80+80 */
+	if (sdata->u.mgd.vht_capa_mask.vht_cap_info &
+	    cpu_to_le32(IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK)) {
+		u32 cap, n;
+
+		n = le32_to_cpu(sdata->u.mgd.vht_capa.vht_cap_info) &
+			IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK;
+		n >>= IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_SHIFT;
+		cap = vht_cap->cap & IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK;
+		cap >>= IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_SHIFT;
+
+		if (n < cap) {
+			vht_cap->cap &=
+				~IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK;
+			vht_cap->cap |=
+				n << IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_SHIFT;
+
+			/* Cannot do short GI 160 if we cannot do 160 or 80+80 */
+			if (n == 0)
+				vht_cap->cap &= ~IEEE80211_VHT_CAP_SHORT_GI_160;
+		}
+	}
+
 	/* Allow user to decrease AMPDU length exponent */
 	if (sdata->u.mgd.vht_capa_mask.vht_cap_info &
 	    cpu_to_le32(IEEE80211_VHT_CAP_MAX_A_MPDU_LENGTH_EXPONENT_MASK)) {
-- 
2.4.11

Re: [PATCH] mac80211: allow overriding station bandwidth.

[Johannes Berg]

On Tue, 2017-02-14 at 13:01 -0800, greearb@candelatech.com wrote:
> From: Ben Greear <greearb@candelatech.com>
> 
> This allows one to disable VHT160 (or 80+80) on hardware
> that might otherwise try to use it.  One potential reason
> to do this is that at least some 160Mhz/80+80 hardware can
> only do 2x2 at 160Mhz, but can do 4x4 at 80Mhz.  And, due to
> driver and firmware issues, it may effectively be limitted
> to 1x1 at 160Mhz for some NICs.

I think the feature is acceptable and don't mind adding that (though
perhaps we should start thinking about making some of these things
debug-only features), but I think the description of why you might want
to do this is misleading - those issues you're describing really should
be solved differently, and I posted the basis for that yesterday.

johannes

Re: [PATCH] mac80211: allow overriding station bandwidth.

[Ben Greear]

On 02/14/2017 11:47 PM, Johannes Berg wrote:
> On Tue, 2017-02-14 at 13:01 -0800, greearb@candelatech.com wrote:
>> From: Ben Greear <greearb@candelatech.com>
>>
>> This allows one to disable VHT160 (or 80+80) on hardware
>> that might otherwise try to use it.  One potential reason
>> to do this is that at least some 160Mhz/80+80 hardware can
>> only do 2x2 at 160Mhz, but can do 4x4 at 80Mhz.  And, due to
>> driver and firmware issues, it may effectively be limitted
>> to 1x1 at 160Mhz for some NICs.
>
> I think the feature is acceptable and don't mind adding that (though
> perhaps we should start thinking about making some of these things
> debug-only features), but I think the description of why you might want
> to do this is misleading - those issues you're describing really should
> be solved differently, and I posted the basis for that yesterday.

Likely for some time remote third-party peers will not update with your patches
to advertise the proper IEs, even if the local system does?

Either way, I suspect that 4x4 VHT80 may perform quite well vs 2x2 VHT160 if
there is any sort of interference on the secondary 80Mhz band...

But, I can just remove the 'why' part of the description entirely if you prefer?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

Re: [PATCH] mac80211: allow overriding station bandwidth.

[Johannes Berg]

> Likely for some time remote third-party peers will not update with
> your patches to advertise the proper IEs, even if the local system
> does?

I think they ought to start doing that pretty soon.

> Either way, I suspect that 4x4 VHT80 may perform quite well vs 2x2
> VHT160 if there is any sort of interference on the secondary 80Mhz
> band...

True. Rate scaling should probably pick that over 160 MHz bandwidth, if
supported. But if, for example, VHT opmode notification restricts
current operation to 2x2, rate scaling should still pick 160 MHz.

> But, I can just remove the 'why' part of the description entirely if
> you prefer?

Yes, I just don't want to give people the wrong idea about this :)

johannes