linux-kernel - Re: [PATCH net v3] net: usb: Remove disruptive netif_wake_queue in rtl8150_set

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Message-ID: <20250924224239.3ec0fcca.michal.pecio@gmail.com>
Date: Wed, 24 Sep 2025 22:42:39 +0200
From: Michal Pecio <michal.pecio@...il.com>
To: Petko Manolov <petkan@...leusys.com>
Cc: I Viswanath <viswanathiyyappan@...il.com>, kuba@...nel.org,
 edumazet@...gle.com, andrew+netdev@...n.ch, davem@...emloft.net,
 pabeni@...hat.com, linux-usb@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
 linux-kernel-mentees@...ts.linux.dev, david.hunter.linux@...il.com,
 syzbot+78cae3f37c62ad092caa@...kaller.appspotmail.com
Subject: Re: [PATCH net v3] net: usb: Remove disruptive netif_wake_queue in
 rtl8150_set_multicast

On Wed, 24 Sep 2025 19:50:55 +0200, Michal Pecio wrote:
> Do you happen to remember what was the reason for padding all TX frames
> to at least 60 bytes?
> 
> This was apparently added in version "v0.5.0 (2002/03/28)".
> 
> I'm yet to test the exact effect of this hack (will the HW really send
> frames with trailing garbage?) and what happens if it's removed (maybe
> nothing bad? or was there a HW bug?), but this part caught my attention
> because I think nowadays some people could consider it "information
> leak" ;) And it looks like a waste of bandwidth at least.

Sorry, stupid question, such frames are illegal.

That being said, I see that other drivers pad them with zeros or
other fixed pattern ('skb_padto(skb, ETH_ZLEN)' seems to be common)
rather than just DMA beyond the specified length.