netdev - Re: [PATCH net-next v6 08/13] net: wwan: t7xx: Add data path interface

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Date:   Tue, 26 Apr 2022 02:55:17 +0300
From:   Sergey Ryazanov <ryazanov.s.a@...il.com>
To:     Ricardo Martinez <ricardo.martinez@...ux.intel.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 v6 08/13] net: wwan: t7xx: Add data path interface

On Fri, Apr 8, 2022 at 1:37 AM Ricardo Martinez
<ricardo.martinez@...ux.intel.com> wrote:
> Data Path Modem AP Interface (DPMAIF) HIF layer provides methods
> for initialization, ISR, control and event handling of TX/RX flows.
>
> DPMAIF TX
> Exposes the 'dmpaif_tx_send_skb' function which can be used by the
> network device to transmit packets.
> The uplink data management uses a Descriptor Ring Buffer (DRB).
> First DRB entry is a message type that will be followed by 1 or more
> normal DRB entries. Message type DRB will hold the skb information
> and each normal DRB entry holds a pointer to the skb payload.
>
> DPMAIF RX
> The downlink buffer management uses Buffer Address Table (BAT) and
> Packet Information Table (PIT) rings.
> The BAT ring holds the address of skb data buffer for the HW to use,
> while the PIT contains metadata about a whole network packet including
> a reference to the BAT entry holding the data buffer address.
> The driver reads the PIT and BAT entries written by the modem, when
> reaching a threshold, the driver will reload the PIT and BAT rings.
>
> Signed-off-by: Haijun Liu <haijun.liu@...iatek.com>
> Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@...el.com>
> Co-developed-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>
> Signed-off-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>
>
> From a WWAN framework perspective:
> Reviewed-by: Loic Poulain <loic.poulain@...aro.org>

Reviewed-by: Sergey Ryazanov <ryazanov.s.a@...il.com>

and a small question below.

> diff --git a/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c b/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> ...
> +static bool t7xx_alloc_and_map_skb_info(const struct dpmaif_ctrl *dpmaif_ctrl,
> +                                       const unsigned int size, struct dpmaif_bat_skb *cur_skb)
> +{
> +       dma_addr_t data_bus_addr;
> +       struct sk_buff *skb;
> +       size_t data_len;
> +
> +       skb = __dev_alloc_skb(size, GFP_KERNEL);
> +       if (!skb)
> +               return false;
> +
> +       data_len = skb_end_pointer(skb) - skb->data;

Earlier you use a nice t7xx_skb_data_area_size() function here, but
now you opencode it. Is it a consequence of t7xx_common.h removing?

I would even encourage you to make this function common and place it
into include/linux/skbuff.h with a dedicated patch and call it
something like skb_data_size(). Surprisingly, there is no such helper
function in the kernel, and several other drivers will benefit from
it:

$ grep -rn 'skb_end_pointer(.*) [-]' drivers/net/
drivers/net/ethernet/marvell/mv643xx_eth.c:628: size =
skb_end_pointer(skb) - skb->data;
drivers/net/ethernet/marvell/pxa168_eth.c:322: size =
skb_end_pointer(skb) - skb->data;
drivers/net/ethernet/micrel/ksz884x.c:4764: if (skb_end_pointer(skb) -
skb->data >= 50) {
drivers/net/ethernet/netronome/nfp/ccm_mbox.c:492: undersize =
max_reply_size - (skb_end_pointer(skb) - skb->data);
drivers/net/ethernet/nvidia/forcedeth.c:2073:
(skb_end_pointer(np->rx_skb[i].skb) -
drivers/net/ethernet/nvidia/forcedeth.c:5238: (skb_end_pointer(tx_skb)
- tx_skb->data),
drivers/net/veth.c:767: frame_sz = skb_end_pointer(skb) - skb->head;
drivers/net/wwan/t7xx/t7xx_hif_cldma.c:106: return
skb_end_pointer(skb) - skb->data;
drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c:160: data_len =
skb_end_pointer(skb) - skb->data;

> +       data_bus_addr = dma_map_single(dpmaif_ctrl->dev, skb->data, data_len, DMA_FROM_DEVICE);
> +       if (dma_mapping_error(dpmaif_ctrl->dev, data_bus_addr)) {
> +               dev_err_ratelimited(dpmaif_ctrl->dev, "DMA mapping error\n");
> +               dev_kfree_skb_any(skb);
> +               return false;
> +       }
> +
> +       cur_skb->skb = skb;
> +       cur_skb->data_bus_addr = data_bus_addr;
> +       cur_skb->data_len = data_len;
> +
> +       return true;
> +}

--
Sergey