netdev - RE: [PATCH v2 net] net: enetc: correct the value of ENETC_RXB

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Message-ID:
 <AM7PR04MB714270BD923D7982895C5CF596F6A@AM7PR04MB7142.eurprd04.prod.outlook.com>
Date: Fri, 17 Oct 2025 07:22:50 +0000
From: Claudiu Manoil <claudiu.manoil@....com>
To: Wei Fang <wei.fang@....com>, Vladimir Oltean <vladimir.oltean@....com>,
	Clark Wang <xiaoning.wang@....com>, "andrew+netdev@...n.ch"
	<andrew+netdev@...n.ch>, "davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>, "kuba@...nel.org"
	<kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>, Frank Li
	<frank.li@....com>
CC: "imx@...ts.linux.dev" <imx@...ts.linux.dev>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 net] net: enetc: correct the value of
 ENETC_RXB_TRUESIZE

> -----Original Message-----
> From: Wei Fang <wei.fang@....com>
> Sent: Thursday, October 16, 2025 11:02 AM
[...]
> Subject: [PATCH v2 net] net: enetc: correct the value of ENETC_RXB_TRUESIZE
> 
> The ENETC RX ring uses the page halves flipping mechanism, each page is
> split into two halves for the RX ring to use. And ENETC_RXB_TRUESIZE is
> defined to 2048 to indicate the size of half a page. However, the page
> size is configurable, for ARM64 platform, PAGE_SIZE is default to 4K,
> but it could be configured to 16K or 64K.
> 
> When PAGE_SIZE is set to 16K or 64K, ENETC_RXB_TRUESIZE is not correct,
> and the RX ring will always use the first half of the page. This is not
> consistent with the description in the relevant kernel doc and commit
> messages.
> 
> This issue is invisible in most cases, but if users want to increase
> PAGE_SIZE to receive a Jumbo frame with a single buffer for some use
> cases, it will not work as expected, because the buffer size of each
> RX BD is fixed to 2048 bytes.
> 
> Based on the above two points, we expect to correct ENETC_RXB_TRUESIZE
> to (PAGE_SIZE >> 1), as described in the comment.
> 
> Fixes: d4fd0404c1c9 ("enetc: Introduce basic PF and VF ENETC ethernet
> drivers")
> Signed-off-by: Wei Fang <wei.fang@....com>

Reviewed-by: Claudiu Manoil <claudiu.manoil@....com>