netdev - Re: [PATCH net-next] net: qualcomm: rmnet: Add side band flow control support

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Message-ID: <5702613e-ea14-40db-2557-7f8363563e33@quicinc.com>
Date: Thu, 21 Sep 2023 09:38:03 -0600
From: "Subash Abhinov Kasiviswanathan (KS)" <quic_subashab@...cinc.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <netdev@...r.kernel.org>
CC: Sean Tranchetti <quic_stranche@...cinc.com>
Subject: Re: [PATCH net-next] net: qualcomm: rmnet: Add side band flow control
 support



On 9/21/2023 4:51 AM, Vadim Fedorenko wrote:
> On 20/09/2023 01:33, Subash Abhinov Kasiviswanathan wrote:
>> Individual rmnet devices map to specific network types such as internet,
>> multimedia messaging services, IP multimedia subsystem etc. Each of
>> these network types may support varying quality of service for different
>> bearers or traffic types.
>>
>                   should it be xa_to_value(p)? otherwise txq is always 1
> 

Agree, this does indeed need to be xa_to_value(p)

>> +static u16 rmnet_vnd_select_queue(struct net_device *dev,
>> +                  struct sk_buff *skb,
>> +                  struct net_device *sb_dev)
>> +{
>> +    struct rmnet_priv *priv = netdev_priv(dev);
>> +    void *p = xa_load(&priv->queue_map, skb->mark);
>> +    u8 txq;
>> +
>> +    if (!p && !xa_is_value(p))
>> +        return 0;
> 
> The check is meaningless. I believe you were thinking about
> 
> if (!p || !xa_is_value(p))
> 
> But the main question: is it even possible to get something from xarray
> that won't pass the check? queue_map is filled in the same code, there 
> is now way (I believe) to change it from anywhere else, right?
> 
>> +
>> +    txq = xa_to_value(p);
>> +
>> +    netdev_dbg(dev, "mark %u -> txq %u\n", skb->mark, txq);
>> +    return (txq < dev->num_tx_queues) ? txq : 0;
>> +}


I'll update these checks as well.
It is not possible for the txq value to exceed the tx_queue limit for a 
given rmnet device.

>