linux-kernel - Re: [PATCH iwl-next v8 08/11] igc: add support to set tx-min-frag-size

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Message-ID: <152e48f6-e68d-4de4-8170-3f35df1ddd1d@linux.intel.com>
Date: Fri, 7 Mar 2025 19:26:05 +0800
From: "Abdul Rahim, Faizal" <faizal.abdul.rahim@...ux.intel.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S . Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Simon Horman <horms@...nel.org>, Russell King <linux@...linux.org.uk>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, Furong Xu <0x1207@...il.com>,
 Russell King <rmk+kernel@...linux.org.uk>,
 Serge Semin <fancer.lancer@...il.com>,
 Xiaolei Wang <xiaolei.wang@...driver.com>,
 Suraj Jaiswal <quic_jsuraj@...cinc.com>,
 Kory Maincent <kory.maincent@...tlin.com>, Gal Pressman <gal@...dia.com>,
 Jesper Nilsson <jesper.nilsson@...s.com>,
 Choong Yong Liang <yong.liang.choong@...ux.intel.com>,
 Chwee-Lin Choong <chwee.lin.choong@...el.com>,
 Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
 Vinicius Costa Gomes <vinicius.gomes@...el.com>,
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, bpf@...r.kernel.org
Subject: Re: [PATCH iwl-next v8 08/11] igc: add support to set
 tx-min-frag-size

On 6/3/2025 8:43 am, Vladimir Oltean wrote:
>> diff --git a/net/ethtool/mm.c b/net/ethtool/mm.c
>> index ad9b40034003..4c395cd949ab 100644
>> --- a/net/ethtool/mm.c
>> +++ b/net/ethtool/mm.c
>> @@ -153,7 +153,7 @@ const struct nla_policy ethnl_mm_set_policy[ETHTOOL_A_MM_MAX + 1] = {
>>   	[ETHTOOL_A_MM_VERIFY_TIME]	= NLA_POLICY_RANGE(NLA_U32, 1, 128),
>>   	[ETHTOOL_A_MM_TX_ENABLED]	= NLA_POLICY_MAX(NLA_U8, 1),
>>   	[ETHTOOL_A_MM_PMAC_ENABLED]	= NLA_POLICY_MAX(NLA_U8, 1),
>> -	[ETHTOOL_A_MM_TX_MIN_FRAG_SIZE]	= NLA_POLICY_RANGE(NLA_U32, 60, 252),
>> +	[ETHTOOL_A_MM_TX_MIN_FRAG_SIZE]	= NLA_POLICY_RANGE(NLA_U32, 60, 256),
> 
> Please make this a separate patch with a reasonably convincing
> justification for any reader, and also state why it is a change that
> will not introduce regressions to the other drivers. It shows that
> you've done the due dilligence of checking that they all use
> ethtool_mm_frag_size_min_to_add(), which errors out on non-standard
> values.
> 
> To be clear, extending the policy from 252 to 256 is just to suppress
> the netlink warning which states that the driver rounds up the minimum
> fragment size, correct? Because even if you pass 252 (the current
> netlink maximum), the driver will still use 256.
> 
I originally changed 252 to 256 because our internal validation failed when 
setting 256 via ethtool. The test case was based on our old kernel OOT 
patches code, but this run was done on the upstreamed FPE framework plus 
this series. After thinking about it, it doesn’t seem right to change this 
just to accommodate the i226 quirk in a common layer when the IEEE standard 
and other devices use 252.

So, we’ll update our validation to use 252 instead. The driver already 
rounds up to 256 anyway. I’ll drop this change in the next revision.

Also, noted your point about being cautious with changes that impact other 
drivers.

Thanks.