RE: [PATCH net v2] net: xilinx: axienet: Fix IRQ coalescing packet count overflow

[Pandey, Radhey Shyam]

> -----Original Message-----
> From: Sean Anderson <sean.anderson@xxxxxxxxx>
> Sent: Tuesday, September 10, 2024 4:39 AM
> To: Pandey, Radhey Shyam <radhey.shyam.pandey@xxxxxxx>; David S .
> Miller <davem@xxxxxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>;
> Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>;
> netdev@xxxxxxxxxxxxxxx
> Cc: Andy Chiu <andy.chiu@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; Simon
> Horman <horms@xxxxxxxxxx>; Ariane Keller <ariane.keller@xxxxxxxxxxxxxx>;
> Daniel Borkmann <daniel@xxxxxxxxxxxxx>; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; Simek, Michal <michal.simek@xxxxxxx>; Sean
> Anderson <sean.anderson@xxxxxxxxx>
> Subject: [PATCH net v2] net: xilinx: axienet: Fix IRQ coalescing packet count
> overflow
> 
> If coalece_count is greater than 255 it will not fit in the register and
> 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.
After this fix - what is o/p we get on rx-frames read? I think silent clamping is not a great 
idea and user won't know about it.  One alternative is to add check in set_coalesc 
count for valid range? (Similar to axienet_ethtools_set_ringparam so that user is notified 
for incorrect range)

> 
> Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>
> 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 */

Adding typecast here looks odd. Any reason for it? 
If needed we do it in specific case where it is required.

> +#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