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Date: Mon, 15 Apr 2024 14:30:20 +0200
From: Niklas =?utf-8?Q?S=C3=B6derlund?= <niklas.soderlund+renesas@ragnatech.se>
To: Paul Barker <paul.barker.ct@bp.renesas.com>
Cc: Sergey Shtylyov <s.shtylyov@omp.ru>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	netdev@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [net-next RFC v3 3/7] net: ravb: Refactor RX ring refill
Message-ID: <20240415123020.GJ3156415@ragnatech.se>
References: <20240415094804.8016-1-paul.barker.ct@bp.renesas.com>
 <20240415094804.8016-4-paul.barker.ct@bp.renesas.com>
 <20240415115755.GH3156415@ragnatech.se>
 <b1d0ca22-de75-4d76-90ba-62c2a57f4301@bp.renesas.com>
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In-Reply-To: <b1d0ca22-de75-4d76-90ba-62c2a57f4301@bp.renesas.com>

On 2024-04-15 13:18:08 +0100, Paul Barker wrote:
> On 15/04/2024 12:57, Niklas Söderlund wrote:
> > Hi Paul,
> > 
> > Thanks for your work, I really like this deduplication of code!
> > 
> > On 2024-04-15 10:48:00 +0100, Paul Barker wrote:
> >> To reduce code duplication, we add a new RX ring refill function which
> >> can handle both the initial RX ring population (which was split between
> >> ravb_ring_init() and ravb_ring_format()) and the RX ring refill after
> >> polling (in ravb_rx()).
> >>
> >> Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
> >> ---
> >>  drivers/net/ethernet/renesas/ravb_main.c | 141 +++++++++--------------
> >>  1 file changed, 52 insertions(+), 89 deletions(-)
> >>
> >> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> >> index 1ac599a044b2..baa01bd81f2d 100644
> >> --- a/drivers/net/ethernet/renesas/ravb_main.c
> >> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> >> @@ -317,35 +317,42 @@ static void ravb_ring_free(struct net_device *ndev, int q)
> >>  	priv->tx_skb[q] = NULL;
> >>  }
> >>  
> >> -static void ravb_rx_ring_format(struct net_device *ndev, int q)
> >> +static u32
> >> +ravb_rx_ring_refill(struct net_device *ndev, int q, u32 count, gfp_t gfp_mask)
> >>  {
> >>  	struct ravb_private *priv = netdev_priv(ndev);
> >> +	const struct ravb_hw_info *info = priv->info;
> >>  	struct ravb_rx_desc *rx_desc;
> >> -	unsigned int rx_ring_size;
> >>  	dma_addr_t dma_addr;
> >> -	unsigned int i;
> >> +	u32 i, entry;
> >>  
> >> -	rx_ring_size = priv->info->rx_desc_size * priv->num_rx_ring[q];
> >> -	memset(priv->rx_ring[q].raw, 0, rx_ring_size);
> >> -	/* Build RX ring buffer */
> >> -	for (i = 0; i < priv->num_rx_ring[q]; i++) {
> >> -		/* RX descriptor */
> >> -		rx_desc = ravb_rx_get_desc(priv, q, i);
> >> -		rx_desc->ds_cc = cpu_to_le16(priv->info->rx_max_desc_use);
> >> -		dma_addr = dma_map_single(ndev->dev.parent, priv->rx_skb[q][i]->data,
> >> -					  priv->info->rx_max_frame_size,
> >> -					  DMA_FROM_DEVICE);
> >> -		/* We just set the data size to 0 for a failed mapping which
> >> -		 * should prevent DMA from happening...
> >> -		 */
> >> -		if (dma_mapping_error(ndev->dev.parent, dma_addr))
> >> -			rx_desc->ds_cc = cpu_to_le16(0);
> >> -		rx_desc->dptr = cpu_to_le32(dma_addr);
> >> +	for (i = 0; i < count; i++) {
> >> +		entry = (priv->dirty_rx[q] + i) % priv->num_rx_ring[q];
> >> +		rx_desc = ravb_rx_get_desc(priv, q, entry);
> >> +		rx_desc->ds_cc = cpu_to_le16(info->rx_max_desc_use);
> >> +
> >> +		if (!priv->rx_skb[q][entry]) {
> >> +			priv->rx_skb[q][entry] = ravb_alloc_skb(ndev, info, gfp_mask);
> >> +			if (!priv->rx_skb[q][entry])
> >> +				break;
> >> +			dma_addr = dma_map_single(ndev->dev.parent,
> >> +						  priv->rx_skb[q][entry]->data,
> >> +						  priv->info->rx_max_frame_size,
> >> +						  DMA_FROM_DEVICE);
> >> +			skb_checksum_none_assert(priv->rx_skb[q][entry]);
> >> +			/* We just set the data size to 0 for a failed mapping
> >> +			 * which should prevent DMA from happening...
> >> +			 */
> >> +			if (dma_mapping_error(ndev->dev.parent, dma_addr))
> >> +				rx_desc->ds_cc = cpu_to_le16(0);
> >> +			rx_desc->dptr = cpu_to_le32(dma_addr);
> >> +		}
> >> +		/* Descriptor type must be set after all the above writes */
> >> +		dma_wmb();
> >>  		rx_desc->die_dt = DT_FEMPTY;
> >>  	}
> >> -	rx_desc = ravb_rx_get_desc(priv, q, i);
> >> -	rx_desc->dptr = cpu_to_le32((u32)priv->rx_desc_dma[q]);
> >> -	rx_desc->die_dt = DT_LINKFIX; /* type */
> >> +
> >> +	return i;
> >>  }
> >>  
> >>  /* Format skb and descriptor buffer for Ethernet AVB */
> >> @@ -353,6 +360,7 @@ static void ravb_ring_format(struct net_device *ndev, int q)
> >>  {
> >>  	struct ravb_private *priv = netdev_priv(ndev);
> >>  	unsigned int num_tx_desc = priv->num_tx_desc;
> >> +	struct ravb_rx_desc *rx_desc;
> >>  	struct ravb_tx_desc *tx_desc;
> >>  	struct ravb_desc *desc;
> >>  	unsigned int tx_ring_size = sizeof(*tx_desc) * priv->num_tx_ring[q] *
> >> @@ -364,8 +372,6 @@ static void ravb_ring_format(struct net_device *ndev, int q)
> >>  	priv->dirty_rx[q] = 0;
> >>  	priv->dirty_tx[q] = 0;
> >>  
> >> -	ravb_rx_ring_format(ndev, q);
> >> -
> >>  	memset(priv->tx_ring[q], 0, tx_ring_size);
> >>  	/* Build TX ring buffer */
> >>  	for (i = 0, tx_desc = priv->tx_ring[q]; i < priv->num_tx_ring[q];
> >> @@ -379,6 +385,14 @@ static void ravb_ring_format(struct net_device *ndev, int q)
> >>  	tx_desc->dptr = cpu_to_le32((u32)priv->tx_desc_dma[q]);
> >>  	tx_desc->die_dt = DT_LINKFIX; /* type */
> >>  
> >> +	/* Regular RX descriptors have already been initialized by
> >> +	 * ravb_rx_ring_refill(), we just need to initialize the final link
> >> +	 * descriptor.
> >> +	 */
> >> +	rx_desc = ravb_rx_get_desc(priv, q, priv->num_rx_ring[q]);
> >> +	rx_desc->dptr = cpu_to_le32((u32)priv->rx_desc_dma[q]);
> >> +	rx_desc->die_dt = DT_LINKFIX; /* type */
> >> +
> > 
> > super-nit: Should you not move this addition up to where you removed the 
> > call to ravb_rx_ring_format()? Before this change the order of things 
> > are,
> > 
> >     /* Init RX ring */
> >     /* Init TX ring */
> >     /* Set RX descriptor base address */
> >     /* Set TX descriptor base address */
> > 
> > 
> > While after it is,
> > 
> >     /* Init TX ring */
> >     /* Init RX ring */
> >     /* Set RX descriptor base address */
> >     /* Set TX descriptor base address */
> > 
> > My OCD is itching ;-)
> 
> Since I'll need to re-spin this series anyway, I may as well tidy that
> up :)
> 
> > 
> >>  	/* RX descriptor base address for best effort */
> >>  	desc = &priv->desc_bat[RX_QUEUE_OFFSET + q];
> >>  	desc->die_dt = DT_LINKFIX; /* type */
> >> @@ -408,11 +422,9 @@ static void *ravb_alloc_rx_desc(struct net_device *ndev, int q)
> >>  static int ravb_ring_init(struct net_device *ndev, int q)
> >>  {
> >>  	struct ravb_private *priv = netdev_priv(ndev);
> >> -	const struct ravb_hw_info *info = priv->info;
> >>  	unsigned int num_tx_desc = priv->num_tx_desc;
> >>  	unsigned int ring_size;
> >> -	struct sk_buff *skb;
> >> -	unsigned int i;
> >> +	u32 num_filled;
> >>  
> >>  	/* Allocate RX and TX skb rings */
> >>  	priv->rx_skb[q] = kcalloc(priv->num_rx_ring[q],
> >> @@ -422,13 +434,6 @@ static int ravb_ring_init(struct net_device *ndev, int q)
> >>  	if (!priv->rx_skb[q] || !priv->tx_skb[q])
> >>  		goto error;
> >>  
> >> -	for (i = 0; i < priv->num_rx_ring[q]; i++) {
> >> -		skb = ravb_alloc_skb(ndev, info, GFP_KERNEL);
> >> -		if (!skb)
> >> -			goto error;
> >> -		priv->rx_skb[q][i] = skb;
> >> -	}
> >> -
> >>  	if (num_tx_desc > 1) {
> >>  		/* Allocate rings for the aligned buffers */
> >>  		priv->tx_align[q] = kmalloc(DPTR_ALIGN * priv->num_tx_ring[q] +
> >> @@ -443,6 +448,13 @@ static int ravb_ring_init(struct net_device *ndev, int q)
> >>  
> >>  	priv->dirty_rx[q] = 0;
> >>  
> >> +	/* Populate RX ring buffer. */
> >> +	ring_size = priv->info->rx_desc_size * priv->num_rx_ring[q];
> >> +	memset(priv->rx_ring[q].raw, 0, ring_size);
> >> +	num_filled = ravb_rx_ring_refill(ndev, q, priv->num_rx_ring[q], GFP_KERNEL);
> >> +	if (num_filled != priv->num_rx_ring[q])
> >> +		goto error;
> >> +
> > 
> > Here you also change the order, but it make sense here as you first deal 
> > with all TX and then all RX ;-)
> 
> The placement here is because we can't call ravb_rx_ring_refill() until
> priv->dirty_rx[q] has been zero'd.
> 
> The init order right now is actually:
>   RX page pool
>   RX buffers
>   TX SKBs
>   RX descriptors
>   RX ring buffer
>   TX descriptors
> 
> So maybe this should be re-ordered.
> 
> I considered breaking this all apart, so ravb_ring_init() would call
> ravb_rx_ring_init()/ravb_tx_ring_init() and ravb_ring_format() would
> call ravb_rx_ring_format()/ravb_tx_ring_format(). There are several
> steps happening for TX & RX in both init and format stages. Does that
> sound cleaner to you?

I think that is a good idea. If you wish I think this can be done on-top 
or break this first part of the series out to a cleanup set, this series 
is quiet large already.

> 
> Thanks,
> 
> -- 
> Paul Barker


-- 
Kind Regards,
Niklas Söderlund