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

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Message-ID: <ed8114c231d1423893d3c90c458f35f3@realtek.com>
Date: Mon, 28 Oct 2024 01:44:21 +0000
From: Ping-Ke Shih <pkshih@...ltek.com>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
CC: "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

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.