Re: [PATCH v7 2/3] Bluetooth: mediatek: Add protocol support for MediaTek serial devices

[Sean Wang <sean.wang@mediatek.com>]

On Fri, 2018-08-03 at 14:51 +0200, Marcel Holtmann wrote:
> Hi Sean,
> 
> >>>>>>> +
> >>>>>>> +static int mtk_hci_wmt_sync(struct hci_dev *hdev, u8 op, u8 flag, u16 plen,
> >>>>>>> +			    const void *param)
> >>>>>>> +{
> >>>>>>> +	struct mtk_hci_wmt_cmd wc;
> >>>>>>> +	struct mtk_wmt_hdr *hdr;
> >>>>>>> +	struct sk_buff *skb;
> >>>>>>> +	u32 hlen;
> >>>>>>> +
> >>>>>>> +	hlen = sizeof(*hdr) + plen;
> >>>>>>> +	if (hlen > 255)
> >>>>>>> +		return -EINVAL;
> >>>>>>> +
> >>>>>>> +	hdr = (struct mtk_wmt_hdr *)&wc;
> >>>>>>> +	hdr->dir = 1;
> >>>>>>> +	hdr->op = op;
> >>>>>>> +	hdr->dlen = cpu_to_le16(plen + 1);
> >>>>>>> +	hdr->flag = flag;
> >>>>>>> +	memcpy(wc.data, param, plen);
> >>>>>>> +
> >>>>>>> +	atomic_inc(&hdev->cmd_cnt);
> >>>>>> 
> >>>>>> Why are you doing this one. It will need a comment here if really needed. However I doubt that this is needed. You are only using it from hdev->setup and hdev->shutdown callbacks.
> >>>>>> 
> >>>>> 
> >>>>> An increment on cmd_cnt is really needed because hci_cmd_work would check whether cmd_cnt is positive and then has a decrement on cmd_cnt before a packet is being sent out.
> >>>>> 
> >>>>> okay will add a comment.
> >>>> 
> >>>> but you are in ->setup callback this time. So if you need this, then all the other ->setup routines would actually fail as well. Either this is leftover from when you did things in ->probe or ->open or this is some thing we might better fix properly in the core instead of papering over it. Can you recheck if this is really needed.
> >>>> 
> >>> 
> >>> I added a counter print and the counter increments as below
> >>> 
> >>> 	/* atomic_inc(&hdev->cmd_cnt); */
> >>>       pr_info("cmd_cnt = %d\n" , atomic_read(&hdev->cmd_cnt));
> >>> 
> >>>       skb = __hci_cmd_sync_ev(hdev, 0xfc6f, hlen, &wc, HCI_VENDOR_PKT,
> >>>                               HCI_INIT_TIMEOUT);
> >>> 
> >>> and the log show up that 
> >>> 
> >>> 
> >>> [  334.049156] Bluetooth: hci0: command 0xfc6f tx timeout
> >>> [  334.054840] cmd_cnt = 0
> >>> [  336.065076] Bluetooth: hci0: command 0xfc6f tx timeout
> >>> [  336.070795] cmd_cnt = 0
> >>> [  338.080997] Bluetooth: hci0: command 0xfc6f tx timeout
> >>> [  338.086683] cmd_cnt = 0
> >>> [  340.096907] Bluetooth: hci0: command 0xfc6f tx timeout
> >>> [  340.102609] cmd_cnt = 0
> >>> [  342.112824] Bluetooth: hci0: command 0xfc6f tx timeout
> >>> [  342.118520] cmd_cnt = 0
> >>> [  344.128747] Bluetooth: hci0: command 0xfc6f tx timeout
> >>> [  344.134454] cmd_cnt = 0
> >>> [  346.144667] Bluetooth: hci0: command 0xfc6f tx timeout
> >>> [  346.150372] cmd_cnt = 0
> >>> 
> >>> 
> >>> The packet is dropped by hci_cmd_work at [1], so I also wondered why the
> >>> other vendor driver works, it seems the counter needs to be incremented
> >>> before every skb is being queued to cmd_q.
> >>> 
> >>> 4257 static void hci_cmd_work(struct work_struct *work)
> >>> 4258 {
> >>> 4259         struct hci_dev *hdev = container_of(work, struct hci_dev, cmd_work);
> >>> 4260         struct sk_buff *skb;
> >>> 4261
> >>> 4262         BT_DBG("%s cmd_cnt %d cmd queued %d", hdev->name,
> >>> 4263                atomic_read(&hdev->cmd_cnt), skb_queue_len(&hdev->cmd_q));
> >>> 4264
> >>> 4265         /* Send queued commands */
> >>> 
> >>> [1]
> >>> 4266         if (atomic_read(&hdev->cmd_cnt)) { /* dropped when cmd_cnt is zero */
> >>> 4267                 skb = skb_dequeue(&hdev->cmd_q);
> >>> 4268                 if (!skb)
> >>> 4269                         return;
> >>> 4270
> >>> 4271                 kfree_skb(hdev->sent_cmd);
> >>> 4272
> >>> 4273                 hdev->sent_cmd = skb_clone(skb, GFP_KERNEL);
> >>> 4274                 if (hdev->sent_cmd) {
> >>> 4275                         atomic_dec(&hdev->cmd_cnt);  /* cmd_cnt-- */
> >>> 4276                         hci_send_frame(hdev, skb);
> >> 
> >> actually the command also needs to better go via the raw_q anyway since it doesn’t come back with the cmd status or cmd complete. You have it waiting for a vendor event. Maybe with is something we need to consider with __hci_cmd_sync_ev anyway.
> >> 
> >> Johan would know best since he wrote that code. Anyway, we should fix that in the core and not have you hack around it.
> >> 
> > 
> > yes, my case is that received event is neither cmd status nor cmd complete. It is completely a vendor event.
> > 
> > if it wants to be solved by the core layer, do you permit that I remove the hack and then send it in the next version?
> 
> we need to have a __hci_raw_sync_ev that uses the hdev->raw_q and waits for the specified event to come back. I never realized that you are missing the cmd status or cmd complete. So this is similar to the original CSR vendor commands which had the same behavior.
> 
> I have the feeling that you hdev->cmd_cnt increment is just hiding the problem here. If you really think that it is not chains any side effects we can merge the driver with a big warning and fix this up. However the clean way would be for you to create a patch that introduces __hci_raw_sync_ev as describe above.

What do you think of this? If I add extra atomic_set 1 on cmd_cnt after driver really got a vendor event back instead of blinding to increment for every packet sent.

the behavior is the same to receive a cmd status or complete. it should not have side effects.

 96         skb = __hci_cmd_sync_ev(hdev, 0xfc6f, hlen, &wc, HCI_VENDOR_PKT,
 97                                 HCI_INIT_TIMEOUT);
 98
 99         if (IS_ERR(skb)) {
100                 int err = PTR_ERR(skb);
101
102                 bt_dev_err(hdev, "Failed to send wmt cmd (%d)", err);
103                 return err;
104         }
105
106         if (!test_bit(HCI_RESET, &hdev->flags)) <<<<<<
107                 atomic_set(&hdev->cmd_cnt, 1);  <<<<<<
108
109         kfree_skb(skb);

> Regards
> 
> Marcel
>