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

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Message-Id: <A6D48D49-52CE-405D-8C5D-C4D54CE67221@holtmann.org>
Date:   Fri, 3 Aug 2018 14:51:03 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Sean Wang <sean.wang@...iatek.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Johan Hedberg <johan.hedberg@...il.com>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/3] Bluetooth: mediatek: Add protocol support for
 MediaTek serial devices

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.

Regards

Marcel