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Commit 613fdf2d authored by Manu Gautam's avatar Manu Gautam
Browse files

USB: gadget: u_bam: Avoid extra context switch possibility in UL 



U_BAM submits UL packets to BAM DMUX from WRITE complete notifier and
epout_completions by scheduling a workqueue. If RX flow control gets
kicked in, due to slow modem uplink, then USB RX requests are not
queued to hardware. And UL packets are then written to BAM DMUX from
work queue that is scheduled from WRITE COMPLETE notify of previous
request. BAM DMUX notify function is already called from workqueue.
This introduces additional context switches and any system level
work queue scheduling latencies may directly affect UL packets
submissions. This scenarios is more likely where modem uplink is
slow as compared to USB transfer rates which always is the case and
this change tries to remove any possibility of BAM_DMUX running out
of UL data (underruns) due to USB driver.

Change-Id: Ifbb50c72bb6a8bd99712d315c3f0e17ca7ea52dd
Signed-off-by: default avatarManu Gautam <mgautam@codeaurora.org>
parent 464ce285

drivers/usb/gadget/u_bam.c

+21 −1
Original line number Diff line number Diff line
@@ -65,6 +65,7 @@ static const enum ipa_client_type usb_cons[BAM2BAM_N_PORTS] = { 


#define DL_INTR_THRESHOLD			20

#define BAM_PENDING_BYTES_LIMIT			(50 * BAM_MUX_RX_REQ_SIZE)

#define BAM_PENDING_BYTES_FCTRL_EN_TSHOLD	(BAM_PENDING_BYTES_LIMIT / 3)



static unsigned int bam_pending_pkts_limit = BAM_PENDING_PKTS_LIMIT;

module_param(bam_pending_pkts_limit, uint, S_IRUGO | S_IWUSR);
@@ -72,6 +73,10 @@ module_param(bam_pending_pkts_limit, uint, S_IRUGO | S_IWUSR); 
static unsigned int bam_pending_bytes_limit = BAM_PENDING_BYTES_LIMIT;

module_param(bam_pending_bytes_limit, uint, S_IRUGO | S_IWUSR);



static unsigned int bam_pending_bytes_fctrl_en_thold =

					BAM_PENDING_BYTES_FCTRL_EN_TSHOLD;

module_param(bam_pending_bytes_fctrl_en_thold, uint, S_IRUGO | S_IWUSR);



static unsigned int bam_mux_tx_pkt_drop_thld = BAM_MUX_TX_PKT_DROP_THRESHOLD;

module_param(bam_mux_tx_pkt_drop_thld, uint, S_IRUGO | S_IWUSR);
@@ -158,6 +163,7 @@ struct bam_ch_info { 
	unsigned int		rx_flow_control_triggered;

	unsigned int		max_num_pkts_pending_with_bam;

	unsigned int		max_bytes_pending_with_bam;

	unsigned int		delayed_bam_mux_write_done;

};



struct gbam_port {
@@ -195,6 +201,7 @@ static void gbam_start_endless_rx(struct gbam_port *port); 
static void gbam_start_endless_tx(struct gbam_port *port);

static int gbam_peer_reset_cb(void *param);

static void gbam_notify(void *p, int event, unsigned long data);

static void gbam_data_write_tobam(struct work_struct *w);



/*---------------misc functions---------------- */

static void gbam_free_requests(struct usb_ep *ep, struct list_head *head)
@@ -499,8 +506,17 @@ void gbam_data_write_done(void *p, struct sk_buff *skb) 


	spin_unlock_irqrestore(&port->port_lock_ul, flags);



	/*

	 * If BAM doesn't have much pending data then push new data from here:

	 * write_complete notify only to avoid any underruns due to wq latency

	 */

	if (d->pending_bytes_with_bam <= bam_pending_bytes_fctrl_en_thold) {

		gbam_data_write_tobam(&d->write_tobam_w);

	} else {

		d->delayed_bam_mux_write_done++;

		queue_work(gbam_wq, &d->write_tobam_w);

	}

}



/* This function should be called with port_lock_ul spinlock acquired */

static bool gbam_ul_bam_limit_reached(struct bam_ch_info *data_ch)
@@ -1834,6 +1850,7 @@ static ssize_t gbam_read_stats(struct file *file, char __user *ubuf, 
				"rx_flow_control_triggered: %u\n"

				"max_num_pkts_pending_with_bam: %u\n"

				"max_bytes_pending_with_bam: %u\n"

				"delayed_bam_mux_write_done: %u\n"

				"tx_buf_len:	 %u\n"

				"rx_buf_len:	 %u\n"

				"data_ch_open:   %d\n"
@@ -1848,6 +1865,7 @@ static ssize_t gbam_read_stats(struct file *file, char __user *ubuf, 
				d->rx_flow_control_triggered,

				d->max_num_pkts_pending_with_bam,

				d->max_bytes_pending_with_bam,

				d->delayed_bam_mux_write_done,

				d->tx_skb_q.qlen, d->rx_skb_q.qlen,

				test_bit(BAM_CH_OPENED, &d->flags),

				test_bit(BAM_CH_READY, &d->flags));
@@ -1892,6 +1910,7 @@ static ssize_t gbam_reset_stats(struct file *file, const char __user *buf, 
		d->rx_flow_control_triggered = 0;

		d->max_num_pkts_pending_with_bam = 0;

		d->max_bytes_pending_with_bam = 0;

		d->delayed_bam_mux_write_done = 0;



		spin_unlock(&port->port_lock_dl);

		spin_unlock_irqrestore(&port->port_lock_ul, flags);
@@ -2087,6 +2106,7 @@ int gbam_connect(struct grmnet *gr, u8 port_num, 
		d->rx_flow_control_triggered = 0;

		d->max_num_pkts_pending_with_bam = 0;

		d->max_bytes_pending_with_bam = 0;

		d->delayed_bam_mux_write_done = 0;

	}



	spin_unlock(&port->port_lock_dl);