netdev - Re: [PATCH net-next v5 06/13] net: wwan: t7xx: Add AT and MBIM WWAN ports

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Date:   Tue, 8 Mar 2022 16:01:53 -0800
From:   "Martinez, Ricardo" <ricardo.martinez@...ux.intel.com>
To:     Sergey Ryazanov <ryazanov.s.a@...il.com>
Cc:     netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Johannes Berg <johannes@...solutions.net>,
        Loic Poulain <loic.poulain@...aro.org>,
        M Chetan Kumar <m.chetan.kumar@...el.com>,
        chandrashekar.devegowda@...el.com,
        Intel Corporation <linuxwwan@...el.com>,
        chiranjeevi.rapolu@...ux.intel.com,
        Haijun Liu (刘海军) 
        <haijun.liu@...iatek.com>, amir.hanania@...el.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        dinesh.sharma@...el.com, eliot.lee@...el.com,
        ilpo.johannes.jarvinen@...el.com, moises.veleta@...el.com,
        pierre-louis.bossart@...el.com, muralidharan.sethuraman@...el.com,
        Soumya.Prakash.Mishra@...el.com, sreehari.kancharla@...el.com,
        madhusmita.sahu@...el.com
Subject: Re: [PATCH net-next v5 06/13] net: wwan: t7xx: Add AT and MBIM WWAN
 ports


On 3/6/2022 6:56 PM, Sergey Ryazanov wrote:
> On Thu, Feb 24, 2022 at 1:35 AM Ricardo Martinez
> <ricardo.martinez@...ux.intel.com> wrote:
>> From: Chandrashekar Devegowda <chandrashekar.devegowda@...el.com>
>>
>> Adds AT and MBIM ports to the port proxy infrastructure.
>> The initialization method is responsible for creating the corresponding
>> ports using the WWAN framework infrastructure. The implemented WWAN port
>> operations are start, stop, and TX.
> [skipped]
>
>> +static int t7xx_port_ctrl_tx(struct wwan_port *port, struct sk_buff *skb)
>> +{
>> +       struct t7xx_port *port_private = wwan_port_get_drvdata(port);
>> +       size_t actual_len, alloc_size, txq_mtu = CLDMA_MTU;
>> +       struct t7xx_port_static *port_static;
>> +       unsigned int len, i, packets;
>> +       struct t7xx_fsm_ctl *ctl;
>> +       enum md_state md_state;
>> +
>> +       len = skb->len;
>> +       if (!len || !port_private->rx_length_th || !port_private->chan_enable)
>> +               return -EINVAL;
>> +
>> +       port_static = port_private->port_static;
>> +       ctl = port_private->t7xx_dev->md->fsm_ctl;
>> +       md_state = t7xx_fsm_get_md_state(ctl);
>> +       if (md_state == MD_STATE_WAITING_FOR_HS1 || md_state == MD_STATE_WAITING_FOR_HS2) {
>> +               dev_warn(port_private->dev, "Cannot write to %s port when md_state=%d\n",
>> +                        port_static->name, md_state);
>> +               return -ENODEV;
>> +       }
>> +
>> +       alloc_size = min_t(size_t, txq_mtu, len + CCCI_HEADROOM);
>> +       actual_len = alloc_size - CCCI_HEADROOM;
>> +       packets = DIV_ROUND_UP(len, txq_mtu - CCCI_HEADROOM);
>> +
>> +       for (i = 0; i < packets; i++) {
>> +               struct ccci_header *ccci_h;
>> +               struct sk_buff *skb_ccci;
>> +               int ret;
>> +
>> +               if (packets > 1 && packets == i + 1) {
>> +                       actual_len = len % (txq_mtu - CCCI_HEADROOM);
>> +                       alloc_size = actual_len + CCCI_HEADROOM;
>> +               }
> Why do you track the packet number? Why not track the offset in the
> passed data? E.g.:
>
> for (off = 0; off < len; off += chunklen) {
>      chunklen = min(len - off, CLDMA_MTU - sizeof(struct ccci_header);
>      skb_ccci = alloc_skb(chunklen + sizeof(struct ccci_header), ...);
>      skb_put_data(skb_ccci, skb->data + off, chunklen);
>      /* Send skb_ccci */
> }
Sure, I'll make that change.
>> +               skb_ccci = __dev_alloc_skb(alloc_size, GFP_KERNEL);
>> +               if (!skb_ccci)
>> +                       return -ENOMEM;
>> +
>> +               ccci_h = skb_put(skb_ccci, sizeof(*ccci_h));
>> +               t7xx_ccci_header_init(ccci_h, 0, actual_len + sizeof(*ccci_h),
>> +                                     port_static->tx_ch, 0);
>> +               skb_put_data(skb_ccci, skb->data + i * (txq_mtu - CCCI_HEADROOM), actual_len);
>> +               t7xx_port_proxy_set_tx_seq_num(port_private, ccci_h);
>> +
>> +               ret = t7xx_port_send_skb_to_md(port_private, skb_ccci);
>> +               if (ret) {
>> +                       dev_kfree_skb_any(skb_ccci);
>> +                       dev_err(port_private->dev, "Write error on %s port, %d\n",
>> +                               port_static->name, ret);
>> +                       return ret;
>> +               }
>> +
>> +               port_private->seq_nums[MTK_TX]++;
> Sequence number tracking as well as CCCI header construction are
> common operations, so why not move them to t7xx_port_send_skb_to_md()?

Sequence number should be set as part of CCCI header construction.

I think it's a bit more readable to initialize the CCCI header right 
after the corresponding skb_put(). Not a big deal, any thoughts?

Note that the upcoming fw update feature doesn't require a CCCI header, 
so we could rename the TX function as t7xx_port_send_ccci_skb_to_md(), 
this would give a hint that it is taking care of the CCCI header.
>> +       }
>> +
>> +       dev_kfree_skb(skb);
>> +       return 0;
>> +}
> --
> Sergey