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Date:   Tue, 10 Mar 2020 09:35:29 +0000
From:   Andre Przywara <andre.przywara@arm.com>
To:     Robert Hancock <hancock@sedsystems.ca>
Cc:     "David S . Miller" <davem@davemloft.net>,
        Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>,
        Michal Simek <michal.simek@xilinx.com>, netdev@vger.kernel.org,
        rmk+kernel@arm.linux.org.uk, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, Andrew Lunn <andrew@lunn.ch>
Subject: Re: [PATCH v2 12/14] net: axienet: Upgrade descriptors to hold
 64-bit addresses
Message-ID: <20200310093529.043bc0a7@donnerap.cambridge.arm.com>
In-Reply-To: <a0cab814-4c93-a59c-55cb-3c5f17c1bcde@sedsystems.ca>
References: <20200309181851.190164-1-andre.przywara@arm.com>
        <20200309181851.190164-13-andre.przywara@arm.com>
        <a0cab814-4c93-a59c-55cb-3c5f17c1bcde@sedsystems.ca>
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On Mon, 9 Mar 2020 12:46:25 -0600
Robert Hancock <hancock@sedsystems.ca> wrote:

Hi,

> On 2020-03-09 12:18 p.m., Andre Przywara wrote:
> > Newer revisions of the AXI DMA IP (>= v7.1) support 64-bit addresses,
> > both for the descriptors itself, as well as for the buffers they are
> > pointing to.
> > This is realised by adding "MSB" words for the next and phys pointer
> > right behind the existing address word, now named "LSB". These MSB words
> > live in formerly reserved areas of the descriptor.
> > 
> > If the hardware supports it, write both words when setting an address.
> > The buffer address is handled by two wrapper functions, the two
> > occasions where we set the next pointers are open coded.
> > 
> > For now this is guarded by a flag which we don't set yet.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > ---
> >  drivers/net/ethernet/xilinx/xilinx_axienet.h  |   9 +-
> >  .../net/ethernet/xilinx/xilinx_axienet_main.c | 113 ++++++++++++------
> >  2 files changed, 83 insertions(+), 39 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet.h b/drivers/net/ethernet/xilinx/xilinx_axienet.h
> > index fb7450ca5c53..84c4c3655516 100644
> > --- a/drivers/net/ethernet/xilinx/xilinx_axienet.h
> > +++ b/drivers/net/ethernet/xilinx/xilinx_axienet.h
> > @@ -328,6 +328,7 @@
> >  #define XAE_FEATURE_PARTIAL_TX_CSUM	(1 << 1)
> >  #define XAE_FEATURE_FULL_RX_CSUM	(1 << 2)
> >  #define XAE_FEATURE_FULL_TX_CSUM	(1 << 3)
> > +#define XAE_FEATURE_DMA_64BIT		(1 << 4)
> >  
> >  #define XAE_NO_CSUM_OFFLOAD		0
> >  
> > @@ -340,9 +341,9 @@
> >  /**
> >   * struct axidma_bd - Axi Dma buffer descriptor layout
> >   * @next:         MM2S/S2MM Next Descriptor Pointer
> > - * @reserved1:    Reserved and not used
> > + * @next_msb:     MM2S/S2MM Next Descriptor Pointer (high 32 bits)
> >   * @phys:         MM2S/S2MM Buffer Address
> > - * @reserved2:    Reserved and not used
> > + * @phys_msb:     MM2S/S2MM Buffer Address (high 32 bits)
> >   * @reserved3:    Reserved and not used
> >   * @reserved4:    Reserved and not used
> >   * @cntrl:        MM2S/S2MM Control value
> > @@ -355,9 +356,9 @@
> >   */
> >  struct axidma_bd {
> >  	u32 next;	/* Physical address of next buffer descriptor */
> > -	u32 reserved1;
> > +	u32 next_msb;	/* high 32 bits for IP >= v7.1, reserved on older IP */
> >  	u32 phys;
> > -	u32 reserved2;
> > +	u32 phys_msb;	/* for IP >= v7.1, reserved for older IP */
> >  	u32 reserved3;
> >  	u32 reserved4;
> >  	u32 cntrl;
> > diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> > index ea44ef4cf288..edee0666d52c 100644
> > --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> > +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> > @@ -153,6 +153,25 @@ static void axienet_dma_out_addr(struct axienet_local *lp, off_t reg,
> >  	axienet_dma_out32(lp, reg, lower_32_bits(addr));
> >  }
> >  
> > +static void desc_set_phys_addr(struct axienet_local *lp, dma_addr_t addr,
> > +			       struct axidma_bd *desc)
> > +{
> > +	desc->phys = lower_32_bits(addr);
> > +	if (lp->features & XAE_FEATURE_DMA_64BIT)
> > +		desc->phys_msb = upper_32_bits(addr);
> > +}
> > +
> > +static dma_addr_t desc_get_phys_addr(struct axienet_local *lp,
> > +				     struct axidma_bd *desc)
> > +{
> > +	dma_addr_t ret = desc->phys;
> > +
> > +	if (lp->features & XAE_FEATURE_DMA_64BIT)
> > +		ret |= (dma_addr_t)desc->phys_msb << 32;  
> 
> Does this compile/work properly on a 32-bit kernel? If dma_addr_t was a
> 32-bit type, I would expect that left-shifting by 32 bits may not do
> what you want. Not sure if there is an inverse to lower_32_bits and
> upper_32_bits macros?

Ah, good point. I compile-tested on 32-bit, but only with ARM32+LPAE, which makes dma_addr_t 64-bit as well.

I couldn't find any suitable macro in kernel.h, but will try << 16 << 16.

Thanks for spotting this (six hours before the build bot)!

Cheers,
Andre

> 
> > +
> > +	return ret;
> > +}
> > +
> >  /**
> >   * axienet_dma_bd_release - Release buffer descriptor rings
> >   * @ndev:	Pointer to the net_device structure
> > @@ -176,6 +195,8 @@ static void axienet_dma_bd_release(struct net_device *ndev)
> >  		return;
> >  
> >  	for (i = 0; i < lp->rx_bd_num; i++) {
> > +		dma_addr_t phys;
> > +
> >  		/* A NULL skb means this descriptor has not been initialised
> >  		 * at all.
> >  		 */
> > @@ -188,9 +209,11 @@ static void axienet_dma_bd_release(struct net_device *ndev)
> >  		 * descriptor size, after it had been successfully allocated.
> >  		 * So a non-zero value in there means we need to unmap it.
> >  		 */
> > -		if (lp->rx_bd_v[i].cntrl)
> > -			dma_unmap_single(ndev->dev.parent, lp->rx_bd_v[i].phys,
> > +		if (lp->rx_bd_v[i].cntrl) {
> > +			phys = desc_get_phys_addr(lp, &lp->rx_bd_v[i]);
> > +			dma_unmap_single(ndev->dev.parent, phys,
> >  					 lp->max_frm_size, DMA_FROM_DEVICE);
> > +		}
> >  	}
> >  
> >  	dma_free_coherent(ndev->dev.parent,
> > @@ -235,29 +258,36 @@ static int axienet_dma_bd_init(struct net_device *ndev)
> >  		goto out;
> >  
> >  	for (i = 0; i < lp->tx_bd_num; i++) {
> > -		lp->tx_bd_v[i].next = lp->tx_bd_p +
> > -				      sizeof(*lp->tx_bd_v) *
> > -				      ((i + 1) % lp->tx_bd_num);
> > +		dma_addr_t addr = lp->tx_bd_p +
> > +				  sizeof(*lp->tx_bd_v) *
> > +				  ((i + 1) % lp->tx_bd_num);
> > +
> > +		lp->tx_bd_v[i].next = lower_32_bits(addr);
> > +		if (lp->features & XAE_FEATURE_DMA_64BIT)
> > +			lp->tx_bd_v[i].next_msb = upper_32_bits(addr);
> >  	}
> >  
> >  	for (i = 0; i < lp->rx_bd_num; i++) {
> > -		lp->rx_bd_v[i].next = lp->rx_bd_p +
> > -				      sizeof(*lp->rx_bd_v) *
> > -				      ((i + 1) % lp->rx_bd_num);
> > +		dma_addr_t addr;
> > +
> > +		addr = lp->rx_bd_p + sizeof(*lp->rx_bd_v) *
> > +			((i + 1) % lp->rx_bd_num);
> > +		lp->rx_bd_v[i].next = lower_32_bits(addr);
> > +		if (lp->features & XAE_FEATURE_DMA_64BIT)
> > +			lp->rx_bd_v[i].next_msb = upper_32_bits(addr);
> >  
> >  		skb = netdev_alloc_skb_ip_align(ndev, lp->max_frm_size);
> >  		if (!skb)
> >  			goto out;
> >  
> >  		lp->rx_bd_v[i].skb = skb;
> > -		lp->rx_bd_v[i].phys = dma_map_single(ndev->dev.parent,
> > -						     skb->data,
> > -						     lp->max_frm_size,
> > -						     DMA_FROM_DEVICE);
> > -		if (dma_mapping_error(ndev->dev.parent, lp->rx_bd_v[i].phys)) {
> > +		addr = dma_map_single(ndev->dev.parent, skb->data,
> > +				      lp->max_frm_size, DMA_FROM_DEVICE);
> > +		if (dma_mapping_error(ndev->dev.parent, addr)) {
> >  			netdev_err(ndev, "DMA mapping error\n");
> >  			goto out;
> >  		}
> > +		desc_set_phys_addr(lp, addr, &lp->rx_bd_v[i]);
> >  
> >  		lp->rx_bd_v[i].cntrl = lp->max_frm_size;
> >  	}
> > @@ -573,6 +603,7 @@ static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
> >  	struct axienet_local *lp = netdev_priv(ndev);
> >  	int max_bds = (nr_bds != -1) ? nr_bds : lp->tx_bd_num;
> >  	struct axidma_bd *cur_p;
> > +	dma_addr_t phys;
> >  	unsigned int status;
> >  	int i;
> >  
> > @@ -586,9 +617,10 @@ static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
> >  		if (nr_bds == -1 && !(status & XAXIDMA_BD_STS_COMPLETE_MASK))
> >  			break;
> >  
> > -		dma_unmap_single(ndev->dev.parent, cur_p->phys,
> > -				(cur_p->cntrl & XAXIDMA_BD_CTRL_LENGTH_MASK),
> > -				DMA_TO_DEVICE);
> > +		phys = desc_get_phys_addr(lp, cur_p);
> > +		dma_unmap_single(ndev->dev.parent, phys,
> > +				 (cur_p->cntrl & XAXIDMA_BD_CTRL_LENGTH_MASK),
> > +				 DMA_TO_DEVICE);
> >  
> >  		if (cur_p->skb && (status & XAXIDMA_BD_STS_COMPLETE_MASK))
> >  			dev_consume_skb_irq(cur_p->skb);
> > @@ -684,7 +716,7 @@ axienet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> >  	u32 csum_start_off;
> >  	u32 csum_index_off;
> >  	skb_frag_t *frag;
> > -	dma_addr_t tail_p;
> > +	dma_addr_t tail_p, phys;
> >  	struct axienet_local *lp = netdev_priv(ndev);
> >  	struct axidma_bd *cur_p;
> >  	u32 orig_tail_ptr = lp->tx_bd_tail;
> > @@ -723,14 +755,15 @@ axienet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> >  		cur_p->app0 |= 2; /* Tx Full Checksum Offload Enabled */
> >  	}
> >  
> > -	cur_p->phys = dma_map_single(ndev->dev.parent, skb->data,
> > -				     skb_headlen(skb), DMA_TO_DEVICE);
> > -	if (unlikely(dma_mapping_error(ndev->dev.parent, cur_p->phys))) {
> > +	phys = dma_map_single(ndev->dev.parent, skb->data,
> > +			      skb_headlen(skb), DMA_TO_DEVICE);
> > +	if (unlikely(dma_mapping_error(ndev->dev.parent, phys))) {
> >  		if (net_ratelimit())
> >  			netdev_err(ndev, "TX DMA mapping error\n");
> >  		ndev->stats.tx_dropped++;
> >  		return NETDEV_TX_OK;
> >  	}
> > +	desc_set_phys_addr(lp, phys, cur_p);
> >  	cur_p->cntrl = skb_headlen(skb) | XAXIDMA_BD_CTRL_TXSOF_MASK;
> >  
> >  	for (ii = 0; ii < num_frag; ii++) {
> > @@ -738,11 +771,11 @@ axienet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> >  			lp->tx_bd_tail = 0;
> >  		cur_p = &lp->tx_bd_v[lp->tx_bd_tail];
> >  		frag = &skb_shinfo(skb)->frags[ii];
> > -		cur_p->phys = dma_map_single(ndev->dev.parent,
> > -					     skb_frag_address(frag),
> > -					     skb_frag_size(frag),
> > -					     DMA_TO_DEVICE);
> > -		if (unlikely(dma_mapping_error(ndev->dev.parent, cur_p->phys))) {
> > +		phys = dma_map_single(ndev->dev.parent,
> > +				      skb_frag_address(frag),
> > +				      skb_frag_size(frag),
> > +				      DMA_TO_DEVICE);
> > +		if (unlikely(dma_mapping_error(ndev->dev.parent, phys))) {
> >  			if (net_ratelimit())
> >  				netdev_err(ndev, "TX DMA mapping error\n");
> >  			ndev->stats.tx_dropped++;
> > @@ -752,6 +785,7 @@ axienet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> >  
> >  			return NETDEV_TX_OK;
> >  		}
> > +		desc_set_phys_addr(lp, phys, cur_p);
> >  		cur_p->cntrl = skb_frag_size(frag);
> >  	}
> >  
> > @@ -790,10 +824,12 @@ static void axienet_recv(struct net_device *ndev)
> >  	cur_p = &lp->rx_bd_v[lp->rx_bd_ci];
> >  
> >  	while ((cur_p->status & XAXIDMA_BD_STS_COMPLETE_MASK)) {
> > +		dma_addr_t phys;
> > +
> >  		tail_p = lp->rx_bd_p + sizeof(*lp->rx_bd_v) * lp->rx_bd_ci;
> >  
> > -		dma_unmap_single(ndev->dev.parent, cur_p->phys,
> > -				 lp->max_frm_size,
> > +		phys = desc_get_phys_addr(lp, cur_p);
> > +		dma_unmap_single(ndev->dev.parent, phys, lp->max_frm_size,
> >  				 DMA_FROM_DEVICE);
> >  
> >  		skb = cur_p->skb;
> > @@ -829,15 +865,16 @@ static void axienet_recv(struct net_device *ndev)
> >  		if (!new_skb)
> >  			return;
> >  
> > -		cur_p->phys = dma_map_single(ndev->dev.parent, new_skb->data,
> > -					     lp->max_frm_size,
> > -					     DMA_FROM_DEVICE);
> > -		if (unlikely(dma_mapping_error(ndev->dev.parent, cur_p->phys))) {
> > +		phys = dma_map_single(ndev->dev.parent, new_skb->data,
> > +				      lp->max_frm_size,
> > +				      DMA_FROM_DEVICE);
> > +		if (unlikely(dma_mapping_error(ndev->dev.parent, phys))) {
> >  			if (net_ratelimit())
> >  				netdev_err(ndev, "RX DMA mapping error\n");
> >  			dev_kfree_skb(new_skb);
> >  			return;
> >  		}
> > +		desc_set_phys_addr(lp, phys, cur_p);
> >  
> >  		cur_p->cntrl = lp->max_frm_size;
> >  		cur_p->status = 0;
> > @@ -882,7 +919,8 @@ static irqreturn_t axienet_tx_irq(int irq, void *_ndev)
> >  		return IRQ_NONE;
> >  	if (status & XAXIDMA_IRQ_ERROR_MASK) {
> >  		dev_err(&ndev->dev, "DMA Tx error 0x%x\n", status);
> > -		dev_err(&ndev->dev, "Current BD is at: 0x%x\n",
> > +		dev_err(&ndev->dev, "Current BD is at: 0x%x%08x\n",
> > +			(lp->tx_bd_v[lp->tx_bd_ci]).phys_msb,
> >  			(lp->tx_bd_v[lp->tx_bd_ci]).phys);
> >  
> >  		cr = axienet_dma_in32(lp, XAXIDMA_TX_CR_OFFSET);
> > @@ -931,7 +969,8 @@ static irqreturn_t axienet_rx_irq(int irq, void *_ndev)
> >  		return IRQ_NONE;
> >  	if (status & XAXIDMA_IRQ_ERROR_MASK) {
> >  		dev_err(&ndev->dev, "DMA Rx error 0x%x\n", status);
> > -		dev_err(&ndev->dev, "Current BD is at: 0x%x\n",
> > +		dev_err(&ndev->dev, "Current BD is at: 0x%x%08x\n",
> > +			(lp->rx_bd_v[lp->rx_bd_ci]).phys_msb,
> >  			(lp->rx_bd_v[lp->rx_bd_ci]).phys);
> >  
> >  		cr = axienet_dma_in32(lp, XAXIDMA_TX_CR_OFFSET);
> > @@ -1633,14 +1672,18 @@ static void axienet_dma_err_handler(struct work_struct *work)
> >  
> >  	for (i = 0; i < lp->tx_bd_num; i++) {
> >  		cur_p = &lp->tx_bd_v[i];
> > -		if (cur_p->cntrl)
> > -			dma_unmap_single(ndev->dev.parent, cur_p->phys,
> > +		if (cur_p->cntrl) {
> > +			dma_addr_t addr = desc_get_phys_addr(lp, cur_p);
> > +
> > +			dma_unmap_single(ndev->dev.parent, addr,
> >  					 (cur_p->cntrl &
> >  					  XAXIDMA_BD_CTRL_LENGTH_MASK),
> >  					 DMA_TO_DEVICE);
> > +		}
> >  		if (cur_p->skb)
> >  			dev_kfree_skb_irq(cur_p->skb);
> >  		cur_p->phys = 0;
> > +		cur_p->phys_msb = 0;
> >  		cur_p->cntrl = 0;
> >  		cur_p->status = 0;
> >  		cur_p->app0 = 0;
> >   
>