[BUG] mt76x0u: Probing issues on Raspberry Pi 3 B+

[Lorenzo Bianconi <lorenzo.bianconi@redhat.com>]

[...]

> In usb_sg_init() urb->num_sgs is set 0 for sg_tablesize = 0 controllers.
> In mt76 we set urb->num_sgs to 1. I thought it is fine, but now I think
> this is bug. We can fix that without changing allocation method and
> still use SG allocation. Attached patch do this, please check if it works
> on rpi. Patch is on top of your error path fixes.
> 
> Stanislaw

> From f79ac0df967d406523d0a1c03a138d1394e7665a Mon Sep 17 00:00:00 2001
> From: Stanislaw Gruszka <sgruszka@redhat.com>
> Date: Tue, 12 Feb 2019 10:02:53 +0100
> Subject: [PATCH] mt76usb: do not set urb->num_sgs to 1 for non SG usb host
>  drivers
> 
> Track number of segments in mt76u_buf structure and do not
> submit urbs with urb->num_sgs = 1 if usb host driver
> sg_tablesize is zero.
> 
> This suppose fix problem of mt76 not working with some usb
> host controllers like dwc2.
> 
> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
> ---
>  drivers/net/wireless/mediatek/mt76/mt76.h |  1 +
>  drivers/net/wireless/mediatek/mt76/usb.c  | 55 ++++++++++++++---------
>  2 files changed, 36 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> index 2e5bcb3fdff7..eadc913c37b6 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> @@ -86,6 +86,7 @@ struct mt76_queue_buf {
>  struct mt76u_buf {
>  	struct mt76_dev *dev;
>  	struct urb *urb;
> +	int num_sgs;
>  	size_t len;
>  	bool done;
>  };
> diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> index a1811c39415e..d82de59ec6dc 100644
> --- a/drivers/net/wireless/mediatek/mt76/usb.c
> +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> @@ -299,14 +299,14 @@ mt76u_fill_rx_sg(struct mt76_dev *dev, struct mt76u_buf *buf,
>  	if (i < nsgs) {
>  		int j;
>  
> -		for (j = nsgs; j < urb->num_sgs; j++)
> +		for (j = nsgs; j < buf->num_sgs; j++)
>  			skb_free_frag(sg_virt(&urb->sg[j]));
> -		urb->num_sgs = i;
> +		buf->num_sgs = i;
>  	}
>  
> -	urb->num_sgs = max_t(int, i, urb->num_sgs);
> -	buf->len = urb->num_sgs * sglen,
> -	sg_init_marker(urb->sg, urb->num_sgs);
> +	buf->num_sgs = max_t(int, i, buf->num_sgs);
> +	buf->len = buf->num_sgs * sglen,
> +	sg_init_marker(urb->sg, buf->num_sgs);
>  
>  	return i ? : -ENOMEM;
>  }
> @@ -325,6 +325,7 @@ int mt76u_buf_alloc(struct mt76_dev *dev, struct mt76u_buf *buf,
>  
>  	sg_init_table(buf->urb->sg, nsgs);
>  	buf->dev = dev;
> +	buf->num_sgs = nsgs;
>  
>  	return mt76u_fill_rx_sg(dev, buf, nsgs, len, sglen);
>  }
> @@ -336,7 +337,7 @@ void mt76u_buf_free(struct mt76u_buf *buf)
>  	struct scatterlist *sg;
>  	int i;
>  
> -	for (i = 0; i < urb->num_sgs; i++) {
> +	for (i = 0; i < buf->num_sgs; i++) {
>  		sg = &urb->sg[i];
>  		if (!sg)
>  			continue;
> @@ -347,9 +348,10 @@ void mt76u_buf_free(struct mt76u_buf *buf)
>  }
>  EXPORT_SYMBOL_GPL(mt76u_buf_free);
>  
> -int mt76u_submit_buf(struct mt76_dev *dev, int dir, int index,
> -		     struct mt76u_buf *buf, gfp_t gfp,
> -		     usb_complete_t complete_fn, void *context)
> +static void
> +mt76u_fill_bulk_urb(struct mt76_dev *dev, int dir, int index,
> +		    struct mt76u_buf *buf, usb_complete_t complete_fn,
> +		    void *context)
>  {
>  	struct usb_interface *intf = to_usb_interface(dev->dev);
>  	struct usb_device *udev = interface_to_usbdev(intf);
> @@ -360,9 +362,25 @@ int mt76u_submit_buf(struct mt76_dev *dev, int dir, int index,
>  	else
>  		pipe = usb_sndbulkpipe(udev, dev->usb.out_ep[index]);
>  
> -	usb_fill_bulk_urb(buf->urb, udev, pipe, NULL, buf->len,
> -			  complete_fn, context);
> +	usb_fill_bulk_urb(buf->urb, udev, pipe, NULL, buf->len, complete_fn,
> +			  context);
> +
> +	if (udev->bus->sg_tablesize > 0) {
> +		buf->urb->num_sgs = buf->num_sgs;
> +	} else {
> +		WARN_ON_ONCE(buf->num_sgs != 1);
> +		/* See usb_sg_init() */
> +		buf->urb->num_sgs = 0;
> +		if (!PageHighMem(sg_page(buf->urb->sg)))
> +			buf->urb->transfer_buffer = sg_virt(buf->urb->sg);

please correct me if I am wrong but doing so we will use transfer_buffer
for 95% of the use cases, right? If so why not keep it simple and always
use it when sg_tablesize is 0 (avoiding SG I/O)?
Btw this is what I proposed with the RFC series actually :) (always use
transfer_buffer in the usb 2.0 case)

Regards,
Lorenzo

> +	}
> +}
>  
> +int mt76u_submit_buf(struct mt76_dev *dev, int dir, int index,
> +		     struct mt76u_buf *buf, gfp_t gfp,
> +		     usb_complete_t complete_fn, void *context)
> +{
> +	mt76u_fill_bulk_urb(dev, dir, index, buf, complete_fn, context);
>  	return usb_submit_urb(buf->urb, gfp);
>  }
>  EXPORT_SYMBOL_GPL(mt76u_submit_buf);
> @@ -672,10 +690,11 @@ static void mt76u_complete_tx(struct urb *urb)
>  }
>  
>  static int
> -mt76u_tx_build_sg(struct sk_buff *skb, struct urb *urb)
> +mt76u_tx_build_sg(struct sk_buff *skb, struct mt76u_buf *buf)
>  {
>  	int nsgs = 1 + skb_shinfo(skb)->nr_frags;
>  	struct sk_buff *iter;
> +	struct urb *urb = buf->urb;
>  
>  	skb_walk_frags(skb, iter)
>  		nsgs += 1 + skb_shinfo(iter)->nr_frags;
> @@ -684,7 +703,8 @@ mt76u_tx_build_sg(struct sk_buff *skb, struct urb *urb)
>  
>  	nsgs = min_t(int, MT_SG_MAX_SIZE, nsgs);
>  	sg_init_marker(urb->sg, nsgs);
> -	urb->num_sgs = nsgs;
> +	buf->num_sgs = nsgs;
> +	buf->len = skb->len;
>  
>  	return skb_to_sgvec_nomark(skb, urb->sg, 0, skb->len);
>  }
> @@ -694,12 +714,9 @@ mt76u_tx_queue_skb(struct mt76_dev *dev, struct mt76_queue *q,
>  		   struct sk_buff *skb, struct mt76_wcid *wcid,
>  		   struct ieee80211_sta *sta)
>  {
> -	struct usb_interface *intf = to_usb_interface(dev->dev);
> -	struct usb_device *udev = interface_to_usbdev(intf);
>  	u8 ep = q2ep(q->hw_idx);
>  	struct mt76u_buf *buf;
>  	u16 idx = q->tail;
> -	unsigned int pipe;
>  	int err;
>  
>  	if (q->queued == q->ndesc)
> @@ -712,13 +729,11 @@ mt76u_tx_queue_skb(struct mt76_dev *dev, struct mt76_queue *q,
>  	buf = &q->entry[idx].ubuf;
>  	buf->done = false;
>  
> -	err = mt76u_tx_build_sg(skb, buf->urb);
> +	err = mt76u_tx_build_sg(skb, buf);
>  	if (err < 0)
>  		return err;
>  
> -	pipe = usb_sndbulkpipe(udev, dev->usb.out_ep[ep]);
> -	usb_fill_bulk_urb(buf->urb, udev, pipe, NULL, skb->len,
> -			  mt76u_complete_tx, buf);
> +	mt76u_fill_bulk_urb(dev, USB_DIR_OUT, ep, buf, mt76u_complete_tx, buf);
>  
>  	q->tail = (q->tail + 1) % q->ndesc;
>  	q->entry[idx].skb = skb;
> -- 
> 2.19.2
>