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

Sean Wang
2018-08-03T18:00:14Z

On Fri, 2018-08-03 at 19:19 +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);
>
> this is even more hackish since the __hci_cmd_sync_ev command is really meant to get a cmd status first before waiting for that event.
>

Understood.

I've stopped the hack in v8. could we merge v8 first ? and then I will a fix up with __hci_raw_sync_ev that uses the hdev->raw_q instead of __hci_cmd_sync_ev in TODO.

> Are all Mediatek vendor commands this way? Or just the ones for loading the firmware? So only the WMT ones?
>

Only the WMT ones, WMT commands/events are usually used in system controlling, for example, global function on/off, firmware download, reset and so on. most only appear on device initialization

> Regards
>
> Marcel
>
>
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