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Message-ID: <dd8369d8-7f3d-467c-afba-abb149bb5942@linux.dev>
Date: Fri, 13 Sep 2024 12:51:45 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
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" <netdev@...r.kernel.org>,
"Gupta, Suraj" <Suraj.Gupta2@....com>,
"Katakam, Harini" <harini.katakam@....com>
Cc: Andy Chiu <andy.chiu@...ive.com>,
"linux-kernel@...r.kernel.org" <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"
<linux-arm-kernel@...ts.infradead.org>, "Simek, Michal"
<michal.simek@....com>
Subject: Re: [PATCH net v2] net: xilinx: axienet: Fix IRQ coalescing packet
count overflow
On 9/11/24 03:01, Pandey, Radhey Shyam wrote:
>> -----Original Message-----
>> From: Sean Anderson <sean.anderson@...ux.dev>
>> Sent: Tuesday, September 10, 2024 4:39 AM
>> 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: 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; Simek, Michal <michal.simek@....com>; Sean
>> Anderson <sean.anderson@...ux.dev>
>> 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@...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 */
>
> Adding typecast here looks odd. Any reason for it?
> If needed we do it in specific case where it is required.
Sorry, I missed this on my first read.
This is necessary for...
>> +#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))) |
this expression. Since min will complain if the types of its arguments
differ. Since coalesce_count_rx is a u32, and integer constants default
to int, I cast the mask to u32 above. Although a U suffix would have
also worked.
--Sean
>> 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
>
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