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wcn36xx: implement flush op to speed up connected scan

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Without ieee80211_ops->flush implemented to empty HW queues, mac80211 will
do a 100ms dead wait after stopping SW queues, before leaving the operating
channel to resume a software connected scan[1].
(see ieee80211_scan_state_resume)

This wait is correctly included in the calculation for whether or not
we've exceeded max off-channel time, as it occurs after sending the null
frame with PS bit set. Thus, with 125 ms max off-channel time we only
have 25 ms of scan time, which technically isn't even enough to scan one
channel (although mac80211 always scans at least one channel per off-
channel window).

Moreover, for passive probes we end up spending at least 100 ms + 111 ms
(IEEE80211_PASSIVE_CHANNEL_TIME) "off-channel"[2], which exceeds the listen
interval of 200 ms that we provide in our association request frame. That's
technically out-of-spec.

[1]: Until recently, wcn36xx performed software (rather than FW-offloaded)
scanning when 5GHz channels are requested. This apparent limitation is now
resolved -- see commit 1395f8a6a4d5 ("wcn36xx: Enable hardware scan offload
for 5Ghz band").
[2]: in quotes because about 100 ms of it is still on-channel but with PS
set

Signed-off-by: Benjamin Li <benl@squareup.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211027170306.555535-3-benl@squareup.com
This commit is contained in:
Benjamin Li 2021-10-27 10:03:04 -07:00 • committed by Kalle Valo
parent df008741dd
commit f02e1cc2a8
3 changed files with 59 additions and 0 deletions
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47
drivers/net/wireless/ath/wcn36xx/dxe.c
View file

@ -834,6 +834,53 @@ unlock:
return ret;
}
static bool _wcn36xx_dxe_tx_channel_is_empty(struct wcn36xx_dxe_ch *ch)
{
unsigned long flags;
struct wcn36xx_dxe_ctl *ctl_bd_start, *ctl_skb_start;
struct wcn36xx_dxe_ctl *ctl_bd, *ctl_skb;
bool ret = true;
spin_lock_irqsave(&ch->lock, flags);
/* Loop through ring buffer looking for nonempty entries. */
ctl_bd_start = ch->head_blk_ctl;
ctl_bd = ctl_bd_start;
ctl_skb_start = ctl_bd_start->next;
ctl_skb = ctl_skb_start;
do {
if (ctl_skb->skb) {
ret = false;
goto unlock;
}
ctl_bd = ctl_skb->next;
ctl_skb = ctl_bd->next;
} while (ctl_skb != ctl_skb_start);
unlock:
spin_unlock_irqrestore(&ch->lock, flags);
return ret;
}
int wcn36xx_dxe_tx_flush(struct wcn36xx *wcn)
{
int i = 0;
/* Called with mac80211 queues stopped. Wait for empty HW queues. */
do {
if (_wcn36xx_dxe_tx_channel_is_empty(&wcn->dxe_tx_l_ch) &&
_wcn36xx_dxe_tx_channel_is_empty(&wcn->dxe_tx_h_ch)) {
return 0;
}
/* This ieee80211_ops callback is specifically allowed to
* sleep.
*/
usleep_range(1000, 1100);
} while (++i < 100);
return -EBUSY;
}
int wcn36xx_dxe_init(struct wcn36xx *wcn)
{
int reg_data = 0, ret;

1
drivers/net/wireless/ath/wcn36xx/dxe.h
View file

@ -466,5 +466,6 @@ int wcn36xx_dxe_tx_frame(struct wcn36xx *wcn,
struct wcn36xx_tx_bd *bd,
struct sk_buff *skb,
bool is_low);
int wcn36xx_dxe_tx_flush(struct wcn36xx *wcn);
void wcn36xx_dxe_tx_ack_ind(struct wcn36xx *wcn, u32 status);
#endif /* _DXE_H_ */

11
drivers/net/wireless/ath/wcn36xx/main.c
View file

@ -1281,6 +1281,16 @@ static void wcn36xx_ipv6_addr_change(struct ieee80211_hw *hw,
}
#endif
static void wcn36xx_flush(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
u32 queues, bool drop)
{
struct wcn36xx *wcn = hw->priv;
if (wcn36xx_dxe_tx_flush(wcn)) {
wcn36xx_err("Failed to flush hardware tx queues\n");
}
}
static const struct ieee80211_ops wcn36xx_ops = {
.start = wcn36xx_start,
.stop = wcn36xx_stop,
@ -1308,6 +1318,7 @@ static const struct ieee80211_ops wcn36xx_ops = {
#if IS_ENABLED(CONFIG_IPV6)
.ipv6_addr_change = wcn36xx_ipv6_addr_change,
#endif
.flush = wcn36xx_flush,
CFG80211_TESTMODE_CMD(wcn36xx_tm_cmd)
};