Re: [PATCH net-next v2 10/18] net: macb: remove illusion about TBQPH/RBQPH being per-queue

[Sean Anderson]

On 6/27/25 05:08, Théo Lebrun wrote:
> The MACB driver acts as if TBQPH/RBQPH are configurable on a per queue
> basis; this is a lie. A single register configures the upper 32 bits of
> each DMA descriptor buffers for all queues.
> 
> Concrete actions:
> 
>  - Drop GEM_TBQPH/GEM_RBQPH macros which have a queue index argument.
>    Only use MACB_TBQPH/MACB_RBQPH constants.
> 
>  - Drop struct macb_queue->TBQPH/RBQPH fields.
> 
>  - In macb_init_buffers(): do a single write to TBQPH and RBQPH for all
>    queues instead of a write per queue.
> 
>  - In macb_tx_error_task(): drop the write to TBQPH.
> 
>  - In macb_alloc_consistent(): if allocations give different upper
>    32-bits, fail. Previously, it would have lead to silent memory
>    corruption as queues would have used the upper 32 bits of the alloc
>    from queue 0 and their own low 32 bits.

While better than silent memory corruption, this is not a good solution
since bringing the netdev up will now randomly fail. Can we allocate the
rings in one contiguous chunk instead?

>  - In macb_suspend(): if we use the tie off descriptor for suspend, do
>    the write once for all queues instead of once per queue.
> 
> Fixes: fff8019a08b6 ("net: macb: Add 64 bit addressing support for GEM")
> Fixes: ae1f2a56d273 ("net: macb: Added support for many RX queues")
> Signed-off-by: Théo Lebrun <theo.lebrun@xxxxxxxxxxx>

As this is a bugfix, can you move it before your cleanup patches? This
will make it easier to backport to stable kernels.

> ---
>  drivers/net/ethernet/cadence/macb.h      |  4 ----
>  drivers/net/ethernet/cadence/macb_main.c | 36 +++++++++++++-------------------
>  2 files changed, 14 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
> index 707b3286a6b8408a3bc4bbbcb1335ae8c3cd95ad..adc70b6efd52b0b11e436c2c95bb5108c40f3490 100644
> --- a/drivers/net/ethernet/cadence/macb.h
> +++ b/drivers/net/ethernet/cadence/macb.h
> @@ -209,10 +209,8 @@
>  
>  #define GEM_ISR(hw_q)		(0x0400 + ((hw_q) << 2))
>  #define GEM_TBQP(hw_q)		(0x0440 + ((hw_q) << 2))
> -#define GEM_TBQPH(hw_q)		(0x04C8)
>  #define GEM_RBQP(hw_q)		(0x0480 + ((hw_q) << 2))
>  #define GEM_RBQS(hw_q)		(0x04A0 + ((hw_q) << 2))
> -#define GEM_RBQPH(hw_q)		(0x04D4)
>  #define GEM_IER(hw_q)		(0x0600 + ((hw_q) << 2))
>  #define GEM_IDR(hw_q)		(0x0620 + ((hw_q) << 2))
>  #define GEM_IMR(hw_q)		(0x0640 + ((hw_q) << 2))
> @@ -1208,10 +1206,8 @@ struct macb_queue {
>  	unsigned int		IDR;
>  	unsigned int		IMR;
>  	unsigned int		TBQP;
> -	unsigned int		TBQPH;
>  	unsigned int		RBQS;
>  	unsigned int		RBQP;
> -	unsigned int		RBQPH;
>  
>  	/* Lock to protect tx_head and tx_tail */
>  	spinlock_t		tx_ptr_lock;
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index a6633e076644089c796453f856a766299bae2ec6..d3b3635998cad095246edf8a75faebbcf7115355 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -482,15 +482,15 @@ static void macb_init_buffers(struct macb *bp)
>  	struct macb_queue *queue;
>  	unsigned int q;
>  
> +	if (macb_dma_is_64b(bp)) {
> +		/* Single register for all queues' high 32 bits. */
> +		macb_writel(bp, RBQPH, upper_32_bits(bp->queues->rx_ring_dma));
> +		macb_writel(bp, TBQPH, upper_32_bits(bp->queues->tx_ring_dma));
> +	}
> +
>  	for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
>  		queue_writel(queue, RBQP, lower_32_bits(queue->rx_ring_dma));
> -		if (macb_dma_is_64b(bp))
> -			queue_writel(queue, RBQPH,
> -				     upper_32_bits(queue->rx_ring_dma));
>  		queue_writel(queue, TBQP, lower_32_bits(queue->tx_ring_dma));
> -		if (macb_dma_is_64b(bp))
> -			queue_writel(queue, TBQPH,
> -				     upper_32_bits(queue->tx_ring_dma));
>  	}
>  }
>  
> @@ -1145,8 +1145,6 @@ static void macb_tx_error_task(struct work_struct *work)
>  
>  	/* Reinitialize the TX desc queue */
>  	queue_writel(queue, TBQP, lower_32_bits(queue->tx_ring_dma));
> -	if (macb_dma_is_64b(bp))
> -		queue_writel(queue, TBQPH, upper_32_bits(queue->tx_ring_dma));
>  	/* Make TX ring reflect state of hardware */
>  	queue->tx_head = 0;
>  	queue->tx_tail = 0;
> @@ -2524,7 +2522,8 @@ static int macb_alloc_consistent(struct macb *bp)
>  		queue->tx_ring = dma_alloc_coherent(&bp->pdev->dev, size,
>  						    &queue->tx_ring_dma,
>  						    GFP_KERNEL);
> -		if (!queue->tx_ring)
> +		if (!queue->tx_ring ||
> +		    upper_32_bits(queue->tx_ring_dma) != upper_32_bits(bp->queues->tx_ring_dma))
>  			goto out_err;
>  		netdev_dbg(bp->dev,
>  			   "Allocated TX ring for queue %u of %d bytes at %08lx (mapped %p)\n",
> @@ -2539,7 +2538,8 @@ static int macb_alloc_consistent(struct macb *bp)
>  		size = RX_RING_BYTES(bp) + bp->rx_bd_rd_prefetch;
>  		queue->rx_ring = dma_alloc_coherent(&bp->pdev->dev, size,
>  						 &queue->rx_ring_dma, GFP_KERNEL);
> -		if (!queue->rx_ring)
> +		if (!queue->rx_ring ||
> +		    upper_32_bits(queue->rx_ring_dma) != upper_32_bits(bp->queues->rx_ring_dma))

Can you write this as bp->queues[0].rx_ring_dma for clarity?

>  			goto out_err;
>  		netdev_dbg(bp->dev,
>  			   "Allocated RX ring of %d bytes at %08lx (mapped %p)\n",
> @@ -4269,10 +4269,6 @@ static int macb_init(struct platform_device *pdev)
>  			queue->TBQP = GEM_TBQP(hw_q - 1);
>  			queue->RBQP = GEM_RBQP(hw_q - 1);
>  			queue->RBQS = GEM_RBQS(hw_q - 1);
> -			if (macb_dma_is_64b(bp)) {
> -				queue->TBQPH = GEM_TBQPH(hw_q - 1);
> -				queue->RBQPH = GEM_RBQPH(hw_q - 1);
> -			}
>  		} else {
>  			/* queue0 uses legacy registers */
>  			queue->ISR  = MACB_ISR;
> @@ -4281,10 +4277,6 @@ static int macb_init(struct platform_device *pdev)
>  			queue->IMR  = MACB_IMR;
>  			queue->TBQP = MACB_TBQP;
>  			queue->RBQP = MACB_RBQP;
> -			if (macb_dma_is_64b(bp)) {
> -				queue->TBQPH = MACB_TBQPH;
> -				queue->RBQPH = MACB_RBQPH;
> -			}
>  		}
>  
>  		/* get irq: here we use the linux queue index, not the hardware
> @@ -5401,6 +5393,10 @@ static int __maybe_unused macb_suspend(struct device *dev)
>  		 */
>  		tmp = macb_readl(bp, NCR);
>  		macb_writel(bp, NCR, tmp & ~(MACB_BIT(TE) | MACB_BIT(RE)));
> +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
> +		if (!(bp->caps & MACB_CAPS_QUEUE_DISABLE))
> +			macb_writel(bp, RBQPH, upper_32_bits(bp->rx_ring_tieoff_dma));
> +#endif
>  		for (q = 0, queue = bp->queues; q < bp->num_queues;
>  		     ++q, ++queue) {
>  			/* Disable RX queues */
> @@ -5410,10 +5406,6 @@ static int __maybe_unused macb_suspend(struct device *dev)
>  				/* Tie off RX queues */
>  				queue_writel(queue, RBQP,
>  					     lower_32_bits(bp->rx_ring_tieoff_dma));
> -#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
> -				queue_writel(queue, RBQPH,
> -					     upper_32_bits(bp->rx_ring_tieoff_dma));
> -#endif
>  			}
>  			/* Disable all interrupts */
>  			queue_writel(queue, IDR, -1);
>