linux-kernel - RE: [PATCH net] net: xilinx: axienet: Fix IRQ coalescing packet count overflow

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Message-ID:
 <MN0PR12MB595374F39CB6F68958004A9DB79C2@MN0PR12MB5953.namprd12.prod.outlook.com>
Date: Wed, 4 Sep 2024 17:19:48 +0000
From: "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>
To: Sean Anderson <sean.anderson@...ux.dev>, "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"
	<netdev@...r.kernel.org>
CC: "Simek, Michal" <michal.simek@....com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, Ariane Keller
	<ariane.keller@....ee.ethz.ch>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>, Andy
 Chiu <andy.chiu@...ive.com>
Subject: RE: [PATCH net] net: xilinx: axienet: Fix IRQ coalescing packet count
 overflow

> -----Original Message-----
> From: Sean Anderson <sean.anderson@...ux.dev>
> Sent: Tuesday, September 3, 2024 11:31 PM
> To: Pandey, Radhey Shyam <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: Simek, Michal <michal.simek@....com>; linux-arm-
> kernel@...ts.infradead.org; Ariane Keller <ariane.keller@....ee.ethz.ch>;
> linux-kernel@...r.kernel.org; Daniel Borkmann <daniel@...earbox.net>;
> Andy Chiu <andy.chiu@...ive.com>; Sean Anderson
> <sean.anderson@...ux.dev>
> Subject: [PATCH net] net: xilinx: axienet: Fix IRQ coalescing packet count
> overflow
> 
> If coalesce_count is greater than 255 it will not fit in the register and
> will overflow. Clamp it to 255 for more-predictable results.
> 
> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet
> driver")
> ---
> 
>  drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 9aeb7b9f3ae4..5f27fc1c4375 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -252,7 +252,8 @@ 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 = (min(lp->coalesce_count_rx, 255) <<
> +			 XAXIDMA_COALESCE_SHIFT) |
>  			XAXIDMA_IRQ_IOC_MASK |

Instead of every time clamping coalesce_count_rx on read I think better 
to do it place where it set in axienet_ethtools_set_coalesce()? It would
also represent the coalesce count state that is reported by get_coalesce()
and same is being used in programming.


> 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 +265,8 @@ 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 = (min(lp->coalesce_count_tx, 255) <<
> +			 XAXIDMA_COALESCE_SHIFT) |
>  			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