linux-kernel - Re: [PATCH] wifi: rtlwifi: Drastically reduce the attempts to read efuse bytes in case of failures

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Message-ID: <61aae4ff-8f80-252e-447a-cd8a51a325a1@igalia.com>
Date: Mon, 28 Oct 2024 11:39:42 -0300
From: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To: Ping-Ke Shih <pkshih@...ltek.com>
Cc: "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
 "kvalo@...nel.org" <kvalo@...nel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "kernel@...ccoli.net" <kernel@...ccoli.net>,
 "kernel-dev@...lia.com" <kernel-dev@...lia.com>,
 "stable@...r.kernel.org" <stable@...r.kernel.org>,
 "syzbot+edd9fe0d3a65b14588d5@...kaller.appspotmail.com"
 <syzbot+edd9fe0d3a65b14588d5@...kaller.appspotmail.com>
Subject: Re: [PATCH] wifi: rtlwifi: Drastically reduce the attempts to read
 efuse bytes in case of failures

On 27/10/2024 22:44, Ping-Ke Shih wrote:
> Guilherme G. Piccoli <gpiccoli@...lia.com> wrote:
>>
>> This procedure for reading efuse bytes relies in a loop that performs an
>> I/O read up to *10k* times in case of failures. We measured the time of
>> the loop inside read_efuse_byte() alone, and in this reproducer (which
>> involves the dummy_hcd emulation layer), it takes 15 seconds each.
> 
> The I/O read of 10k times is to polling if efuse is ready, and then following
> statement is to actually read efuse content back. For USB devices, I/O is
> slow, so it might be fine to reduce retry times. But For PCIE devices,
> I think this will be risky without testing with real hardware.
> 
> Possible way is to use "rtlhal->interface == INTF_PCI" to keep original times
> for PCIE devices, and only reduce retry times for USB devices. But USB can
> operate on USB-2/-3 modes, so maybe still need experiments with real hardware 
> to get reasonable retry times. 
> 

Thanks a bunch for the review and extra details Ping-Ke Shih!

The idea of guarding with "rtlhal->interface == INTF_PCI" is very good
and I can implement in a V2.

But can you help me on finding a USB adapter that runs this path? If you
know a commodity model that uses this specific driver, could you point
me so I can buy one for testing?

Meanwhile I'll try to find a model based on some kernel reports online,
hope I can!

Cheers,

Guilherme