netdev - Re: [PATCH v2 net-next 5/9] net: mvneta: add multi buffer support to XDP

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Date:   Sun, 6 Sep 2020 10:43:43 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Shay Agroskin <shayagr@...zon.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, davem@...emloft.net,
        lorenzo.bianconi@...hat.com, brouer@...hat.com,
        echaudro@...hat.com, sameehj@...zon.com, kuba@...nel.org,
        john.fastabend@...il.com, daniel@...earbox.net, ast@...nel.org
Subject: Re: [PATCH v2 net-next 5/9] net: mvneta: add multi buffer support to
 XDP_TX

> 
> Lorenzo Bianconi <lorenzo@...nel.org> writes:
> 

[...]

> > -	buf->xdpf = xdpf;
> > -	tx_desc->command = MVNETA_TXD_FLZ_DESC;
> > -	tx_desc->buf_phys_addr = dma_addr;
> > -	tx_desc->data_size = xdpf->len;
> > +	/*last descriptor */
> > +	if (tx_desc)
> > +		tx_desc->command |= MVNETA_TXD_L_DESC | MVNETA_TXD_Z_PAD;
> 
>        When is this condition not taken ? You initialize tx_desc        to
> NULL, but it seems to me like you always set it inside        the for loop
> to the output of mvneta_txq_next_desc_get()        which doesn't look like
> it returns NULL. The for loop runs 1 iteration or `sinfo->nr_frage + 1`
> iterations (which also equals or larger than 1).

ack, right. I will fix it in v3.

Regards,
Lorenzo

> 
> > -	mvneta_txq_inc_put(txq);
> > -	txq->pending++;
> > -	txq->count++;
> > +	txq->pending += num_frames;
> > +	txq->count += num_frames;
> >  	return MVNETA_XDP_TX;
> >  }
> 

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