netdev - Re: [PATCH net v3] net: airoha: Add missing filed to ppe_mbox

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Message-ID: <20250424170929.3fb25bb8@kernel.org>
Date: Thu, 24 Apr 2025 17:09:29 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jacob Keller <jacob.e.keller@...el.com>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>, Andrew Lunn
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 <linux-arm-kernel@...ts.infradead.org>,
 <linux-mediatek@...ts.infradead.org>, <netdev@...r.kernel.org>, Simon
 Horman <horms@...nel.org>
Subject: Re: [PATCH net v3] net: airoha: Add missing filed to ppe_mbox_data
 struct

On Wed, 23 Apr 2025 09:34:49 -0700 Jacob Keller wrote:
> >> One oddity here is that the structure is not marked __packed. This
> >> addition of a u8 means there will be a 3-byte gap on platforms which
> >> have a 4-byte integer... It feels very weird these are ints and not s32
> >> or something to fully clarify the sizes.  
> > 
> > yes, you are right. Let's hold on for a while with this patch and let me ask
> > Airoha folks if we can "pack" the struct in the NPU firmware binary so we can use
> > __packed attribute here. In any case I will use "u32" instead of "int" in the next
> > version.  
> 
> Sure. Also, if firmware already has this layout fixed, you could add the
> 3 padding bytes marked as reserved to make it more obvious they exist
> without needing to remember the rules for how the members will align.

+1 FWIW, mark the padding explicitly is good, but don't make everything
misaligned with __packed