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Message-ID: <20240904160013.GX4792@kernel.org>
Date: Wed, 4 Sep 2024 17:00:13 +0100
From: Simon Horman <horms@...nel.org>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: 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, Michal Simek <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>
Subject: Re: [PATCH net] net: xilinx: axienet: Fix IRQ coalescing packet
count overflow
On Tue, Sep 03, 2024 at 02:00:59PM -0400, Sean Anderson wrote:
> 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.
Hi Sean,
Can this occur in practice?
>
> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
nit: I think it is usual for the order of these tags to be reversed.
> ---
>
> 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 | XAXIDMA_IRQ_ERROR_MASK;
nit: it would be nice to avoid using a naked 255 here.
Perhaps: #define XAXIDMA_COALESCE_MAX 0xff
> /* 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
>
>
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