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

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Date:   Thu, 21 Apr 2022 13:54:08 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Ricardo Martinez <ricardo.martinez@...ux.intel.com>
cc:     netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        kuba@...nel.org, davem@...emloft.net, johannes@...solutions.net,
        ryazanov.s.a@...il.com, loic.poulain@...aro.org,
        m.chetan.kumar@...el.com, chandrashekar.devegowda@...el.com,
        linuxwwan@...el.com, chiranjeevi.rapolu@...ux.intel.com,
        haijun.liu@...iatek.com, amir.hanania@...el.com,
        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 Thu, 7 Apr 2022, Ricardo Martinez wrote:

> From: Haijun Liu <haijun.liu@...iatek.com>
> 
> 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>

> +       if (txq->tx_skb_head.qlen >= txq->tx_list_max_len)
> +               goto report_full_state;
> +
> +       skb_cb = T7XX_SKB_CB(skb);
> +       skb_cb->txq_number = txq_number;
> +       skb_queue_tail(&txq->tx_skb_head, skb);
> +       wake_up(&dpmaif_ctrl->tx_wq);
> +       return 0;
> +
> +report_full_state:
> +       callbacks = dpmaif_ctrl->callbacks;
> +       callbacks->state_notify(dpmaif_ctrl->t7xx_dev, DMPAIF_TXQ_STATE_FULL, txq_number>
> +       return -EBUSY;
> +}

Should this actually report full earlier so that the queue can be stopped 
before NETDEV_TX_BUSY has to be returned (by the callers in 09/13)?
(see Documentation/networking/driver.rst)

> +		/* Wait for active Tx to be doneg */

doneg -> done

> +struct dpmaif_drb {
> +	__le32 header;
> +	union {
> +		struct {
> +			__le32 data_addr_l;
> +			__le32 data_addr_h;
> +			__le32 reserved;
> +		} pd;
> +		struct {
> +			__le32 msg_hdr;
> +			__le32 reserved1;
> +			__le32 reserved2;
> +		} msg;
> +	};
> +};

"reserved" and "reserved2" could be placed outside of the union
as they have the same offset.


-- 
 i.