From: Vladimir Oltean <olteanv@gmail.com>
To: "Clément Léger" <clement.leger@bootlin.com>
Cc: "Andrew Lunn" <andrew@lunn.ch>,
"Vivien Didelot" <vivien.didelot@gmail.com>,
"Florian Fainelli" <f.fainelli@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Rob Herring" <robh+dt@kernel.org>,
"Krzysztof Kozlowski" <krzk+dt@kernel.org>,
"Geert Uytterhoeven" <geert+renesas@glider.be>,
"Magnus Damm" <magnus.damm@gmail.com>,
"Heiner Kallweit" <hkallweit1@gmail.com>,
"Russell King" <linux@armlinux.org.uk>,
"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
"Herve Codina" <herve.codina@bootlin.com>,
"Miquèl Raynal" <miquel.raynal@bootlin.com>,
"Milan Stevanovic" <milan.stevanovic@se.com>,
"Jimmy Lalande" <jimmy.lalande@se.com>,
linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
linux-renesas-soc@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH net-next 02/12] net: dsa: add Renesas RZ/N1 switch tag driver
Date: Thu, 14 Apr 2022 18:11:46 +0300 [thread overview]
Message-ID: <20220414151146.a2fncklswo6utiyd@skbuf> (raw)
In-Reply-To: <20220414163546.3f6c5157@fixe.home>
On Thu, Apr 14, 2022 at 04:35:46PM +0200, Clément Léger wrote:
> > Please keep variable declarations sorted in decreasing order of line
> > length (applies throughout the patch series, I won't repeat this comment).
>
> Acked, both PCS and DSA driver are ok with that rule. Missed that one
> though.
Are you sure? Because a5psw_port_stp_state_set() says otherwise.
> > sizeof(tag), to be consistent with the other use of sizeof() above?
> > Although, hmm, I think you could get away with editing "ptag" in place.
>
> I was not sure of the alignment guarantee I would have here. If the
> VLAN header is guaranteed to be aligned on 2 bytes, then I guess it's
> ok to do that in-place.
If I look at Documentation/core-api/unaligned-memory-access.rst
| Alignment vs. Networking
| ========================
|
| On architectures that require aligned loads, networking requires that the IP
| header is aligned on a four-byte boundary to optimise the IP stack. For
| regular ethernet hardware, the constant NET_IP_ALIGN is used. On most
| architectures this constant has the value 2 because the normal ethernet
| header is 14 bytes long, so in order to get proper alignment one needs to
| DMA to an address which can be expressed as 4*n + 2. One notable exception
| here is powerpc which defines NET_IP_ALIGN to 0 because DMA to unaligned
| addresses can be very expensive and dwarf the cost of unaligned loads.
Your struct a5psw_tag *ptag starts at 10 bytes (8 for tag, 2 for Ethertype)
before the IP header, so I'm thinking it is aligned at a 2 byte boundary
as well. A VLAN header between the DSA header and the IP header should
also not affect that alignment, since its length is 4 bytes.
If "ctrl_tag" is aligned at a 4 byte boundary - 10, it means "ctrl_data"
is aligned at a 4 byte boundary - 8, so also a 4 byte boundary.
But "ctrl_data2" is aligned at a 4 byte boundary + 2, so you might want
to break up the u32 access into 2 u16 accesses, just to be on the safe
side?
next prev parent reply other threads:[~2022-04-14 15:46 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-14 12:22 [PATCH net-next 00/12] add support for Renesas RZ/N1 ethernet subsystem devices Clément Léger
2022-04-14 12:22 ` [PATCH net-next 01/12] net: dsa: add support for Renesas RZ/N1 A5PSW switch tag code Clément Léger
2022-04-14 13:44 ` Vladimir Oltean
2022-04-14 12:22 ` [PATCH net-next 02/12] net: dsa: add Renesas RZ/N1 switch tag driver Clément Léger
2022-04-14 14:22 ` Vladimir Oltean
2022-04-14 14:35 ` Clément Léger
2022-04-14 15:11 ` Vladimir Oltean [this message]
2022-04-14 16:18 ` Clément Léger
2022-04-14 16:23 ` Russell King (Oracle)
2022-04-15 7:23 ` Clément Léger
2022-04-14 22:50 ` Andrew Lunn
2022-04-14 12:22 ` [PATCH net-next 03/12] dt-bindings: net: pcs: add bindings for Renesas RZ/N1 MII converter Clément Léger
2022-04-14 18:59 ` Rob Herring
2022-04-19 13:43 ` Rob Herring
2022-04-19 15:00 ` Clément Léger
2022-04-20 20:11 ` Rob Herring
2022-04-21 7:35 ` Clément Léger
2022-04-14 12:22 ` [PATCH net-next 04/12] net: pcs: add Renesas MII converter driver Clément Léger
2022-04-14 12:49 ` Russell King (Oracle)
2022-04-14 15:14 ` Clément Léger
2022-04-20 13:25 ` Geert Uytterhoeven
2022-04-14 12:22 ` [PATCH net-next 05/12] dt-bindings: net: dsa: add bindings for Renesas RZ/N1 Advanced 5 port switch Clément Léger
2022-04-14 18:59 ` Rob Herring
2022-04-27 12:20 ` Geert Uytterhoeven
2022-04-27 12:56 ` Clément Léger
2022-04-14 12:22 ` [PATCH net-next 06/12] net: dsa: rzn1-a5psw: add Renesas RZ/N1 advanced 5 port switch driver Clément Léger
2022-04-14 13:02 ` Russell King (Oracle)
2022-04-15 8:40 ` Clément Léger
2022-04-15 8:52 ` Russell King (Oracle)
2022-04-14 14:47 ` Vladimir Oltean
2022-04-14 17:51 ` Andrew Lunn
2022-04-15 9:34 ` Clément Léger
2022-04-15 10:55 ` Vladimir Oltean
2022-04-15 11:02 ` Russell King (Oracle)
2022-04-15 11:14 ` Vladimir Oltean
2022-04-15 11:23 ` Russell King (Oracle)
2022-04-15 12:01 ` Vladimir Oltean
2022-04-15 11:05 ` Vladimir Oltean
2022-04-15 12:31 ` Clément Léger
2022-04-15 12:28 ` Clément Léger
2022-04-15 12:41 ` Vladimir Oltean
2022-04-14 17:55 ` Andrew Lunn
2022-04-15 12:33 ` Clément Léger
2022-04-14 12:22 ` [PATCH net-next 07/12] net: dsa: rzn1-a5psw: add statistics support Clément Léger
2022-04-14 17:34 ` Vladimir Oltean
2022-04-15 12:42 ` Clément Léger
2022-04-14 23:16 ` Andrew Lunn
2022-04-15 12:04 ` Clément Léger
2022-04-15 13:37 ` Andrew Lunn
2022-04-15 13:44 ` Clément Léger
2022-04-14 12:22 ` [PATCH net-next 08/12] net: dsa: rzn1-a5psw: add FDB support Clément Léger
2022-04-14 17:51 ` Vladimir Oltean
2022-04-20 8:16 ` Clément Léger
2022-04-20 19:52 ` Vladimir Oltean
2022-04-21 7:38 ` Clément Léger
2022-04-14 12:22 ` [PATCH net-next 09/12] ARM: dts: r9a06g032: describe MII converter Clément Léger
2022-04-14 23:22 ` Andrew Lunn
2022-04-15 8:24 ` Clément Léger
2022-04-15 14:16 ` Andrew Lunn
2022-04-15 14:38 ` Clément Léger
2022-04-15 15:12 ` Andrew Lunn
2022-04-15 15:29 ` Clément Léger
2022-04-15 16:19 ` Andrew Lunn
2022-04-15 16:45 ` Clément Léger
2022-04-16 13:48 ` Andrew Lunn
2022-04-19 9:03 ` Clément Léger
2022-04-19 12:57 ` Andrew Lunn
2022-04-20 20:16 ` Rob Herring
2022-04-14 12:22 ` [PATCH net-next 10/12] ARM: dts: r9a06g032: describe GMAC2 Clément Léger
2022-04-21 9:31 ` Geert Uytterhoeven
2022-04-14 12:22 ` [PATCH net-next 11/12] ARM: dts: r9a06g032: describe switch Clément Léger
2022-04-21 9:34 ` Geert Uytterhoeven
2022-04-14 12:22 ` [PATCH net-next 12/12] MAINTAINERS: add Renesas RZ/N1 switch related driver entry Clément Léger
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