netdev - Re: [PATCH net v2] net: xilinx: axienet: Fix IRQ coalescing packet count overflow

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Message-ID: <4f33691d-4997-4145-9cfe-f8e5a187e4ac@amd.com>
Date: Mon, 9 Sep 2024 17:51:07 -0700
From: "Nelson, Shannon" <shannon.nelson@....com>
To: Sean Anderson <sean.anderson@...ux.dev>,
 Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc: Andy Chiu <andy.chiu@...ive.com>, linux-kernel@...r.kernel.org,
 Simon Horman <horms@...nel.org>, Ariane Keller
 <ariane.keller@....ee.ethz.ch>, Daniel Borkmann <daniel@...earbox.net>,
 linux-arm-kernel@...ts.infradead.org, Michal Simek <michal.simek@....com>
Subject: Re: [PATCH net v2] net: xilinx: axienet: Fix IRQ coalescing packet
 count overflow

On 9/9/2024 4:09 PM, Sean Anderson wrote:
> 
> If coalece_count is greater than 255 it will not fit in the register and

s/coalece_count/coalesce_count/

Otherwise

Reviewed-by: Shannon Nelson <shannon.nelson@....com>


> will overflow. This can be reproduced by running
> 
>      # ethtool -C ethX rx-frames 256
> 
> which will result in a timeout of 0us instead. Fix this by clamping the
> counts to the maximum value.
> 
> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
> ---
> 
> Changes in v2:
> - Use FIELD_MAX to extract the max value from the mask
> - Expand the commit message with an example on how to reproduce this
>    issue
> 
>   drivers/net/ethernet/xilinx/xilinx_axienet.h      | 5 ++---
>   drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 8 ++++++--
>   2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet.h b/drivers/net/ethernet/xilinx/xilinx_axienet.h
> index 1223fcc1a8da..54db69893565 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet.h
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet.h
> @@ -109,11 +109,10 @@
>   #define XAXIDMA_BD_CTRL_TXEOF_MASK     0x04000000 /* Last tx packet */
>   #define XAXIDMA_BD_CTRL_ALL_MASK       0x0C000000 /* All control bits */
> 
> -#define XAXIDMA_DELAY_MASK             0xFF000000 /* Delay timeout counter */
> -#define XAXIDMA_COALESCE_MASK          0x00FF0000 /* Coalesce counter */
> +#define XAXIDMA_DELAY_MASK             ((u32)0xFF000000) /* Delay timeout counter */
> +#define XAXIDMA_COALESCE_MASK          ((u32)0x00FF0000) /* Coalesce counter */
> 
>   #define XAXIDMA_DELAY_SHIFT            24
> -#define XAXIDMA_COALESCE_SHIFT         16
> 
>   #define XAXIDMA_IRQ_IOC_MASK           0x00001000 /* Completion intr */
>   #define XAXIDMA_IRQ_DELAY_MASK         0x00002000 /* Delay interrupt */
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 9eb300fc3590..89b63695293d 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -252,7 +252,9 @@ static u32 axienet_usec_to_timer(struct axienet_local *lp, u32 coalesce_usec)
>   static void axienet_dma_start(struct axienet_local *lp)
>   {
>          /* Start updating the Rx channel control register */
> -       lp->rx_dma_cr = (lp->coalesce_count_rx << XAXIDMA_COALESCE_SHIFT) |
> +       lp->rx_dma_cr = FIELD_PREP(XAXIDMA_COALESCE_MASK,
> +                                  min(lp->coalesce_count_rx,
> +                                      FIELD_MAX(XAXIDMA_COALESCE_MASK))) |
>                          XAXIDMA_IRQ_IOC_MASK | XAXIDMA_IRQ_ERROR_MASK;
>          /* Only set interrupt delay timer if not generating an interrupt on
>           * the first RX packet. Otherwise leave at 0 to disable delay interrupt.
> @@ -264,7 +266,9 @@ static void axienet_dma_start(struct axienet_local *lp)
>          axienet_dma_out32(lp, XAXIDMA_RX_CR_OFFSET, lp->rx_dma_cr);
> 
>          /* Start updating the Tx channel control register */
> -       lp->tx_dma_cr = (lp->coalesce_count_tx << XAXIDMA_COALESCE_SHIFT) |
> +       lp->tx_dma_cr = FIELD_PREP(XAXIDMA_COALESCE_MASK,
> +                                  min(lp->coalesce_count_tx,
> +                                      FIELD_MAX(XAXIDMA_COALESCE_MASK))) |
>                          XAXIDMA_IRQ_IOC_MASK | XAXIDMA_IRQ_ERROR_MASK;
>          /* Only set interrupt delay timer if not generating an interrupt on
>           * the first TX packet. Otherwise leave at 0 to disable delay interrupt.
> --
> 2.35.1.1320.gc452695387.dirty
> 
>