linux-kernel - Re: [regression] Significant WiFi Speed Reduction with Kernel Versions

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Message-ID: <db6e127f5f7cfaf76bbf4438ae8962993f4aba03.camel@sipsolutions.net>
Date: Wed, 05 Mar 2025 13:56:19 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Bjorn Helgaas <helgaas@...nel.org>, Miri Korenblit
	 <miriam.rachel.korenblit@...el.com>, emmanuel.grumbach@...el.com
Cc: "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>, LKML
	 <linux-kernel@...r.kernel.org>
Subject: Re: [regression] Significant WiFi Speed Reduction with Kernel
 Versions > 6.8.12 on Intel Wi-Fi 6 AX203

[removing folks no longer involved]

Hi,

So ... it's complicated, but I think it's a bug.

> 4886460c4d15 ("iwlwifi: Fix IWL_SUBDEVICE_NO_160 macro to use the
> correct bit.") updated IWL_SUBDEVICE_NO_160() to identify devices that
> should not support 160MHz:
> 
>   -#define IWL_SUBDEVICE_NO_160(subdevice)        ((u16)((subdevice) & 0x0100) >> 9)
>   +#define IWL_SUBDEVICE_NO_160(subdevice)        ((u16)((subdevice) & 0x0200) >> 9)

I'm not even entirely sure this logic is correct; however, it doesn't
really matter.

> The submitter's device has Subdevice ID 0x1652.  Prior to
> 4886460c4d15, that did not match IWL_SUBDEVICE_NO_160(), but
> afterwards it does:
> 
>   0000:00:14.3 Network controller [0280]: Intel Corporation Alder Lake-P PCH CNVi WiFi [8086:51f0] (rev 01)
>     Subsystem: Rivet Networks Dual Band Wi-Fi 6(802.11ax) Killer AX1650i 160MHz 2x2 [Cyclone Peak] [1a56:1652]

According to our internal information (SKUMAP-362, for the Intel folks
who know what that means), this name is correct, it should be 160 Mhz.

> But apparently it wasn't until 84ec2d2e960f ("wifi: iwlwifi: disable
> 160 MHz based on subsystem device ID"), that 160MHz support actually
> got disabled for devices that match IWL_SUBDEVICE_NO_160():

I've also found information elsewhere (WREQ-269994) that the whole
IWL_SUBDEVICE_NO_160 (now actually a bit different to take no-320 into
account on newer hardware) is *not* applicable to "Killer" branded
devices at all.

So I think it's a bug, but I'm not sure right now *how* we can fix it.
It looks like our matching must skip the bandwidth restriction thing for
Killer devices.

johannes