Subject: Re: [PATCH v3 00/13] rtw88: mac80211 driver for Realtek 802.11ac
 wireless network chips
To:     =?UTF-8?B?6I6K5b2l5a6j?= <yhchuang@realtek.com>
Cc:     Pkshih <pkshih@realtek.com>, tehuang@realtek.com,
        briannorris@chromium.org, sgruszka@redhat.com,
        linux-wireless@vger.kernel.org
References: <1548654407-28469-1-git-send-email-yhchuang@realtek.com>
From:   Larry Finger <Larry.Finger@lwfinger.net>
Message-ID: <043aedf4-0ed4-e128-3cd2-242aaef128f6@lwfinger.net>
Date:   Mon, 28 Jan 2019 14:56:51 -0600
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Tony,

I had not tested rtw88 for some time, so I built a kernel with the V3 patches 
and found that rtw88 crashed with a NULL pointer dereference. I did some 
debugging and found that the problem was in routine rtw_chip_efuse_enable() 
where fw->firmware was NULL.

Next I verified that rtw_load_firmware() had been called, which gave a clue that 
the firmware had not finished loading by the time rtw_chip_efuse_enable() was 
called. By adding a wait_for_completion() call before the 
rtw_download_firmware() call, the problem was fixed. The problem was a race 
between calling rtw_chip_efuse_enable() and the firmware load from disk. 
Obviously, the speed ratio between my CPU and the disk system is much different 
on my laptop than on your test machines, thus I have the problem.

The patch I used is attached.

Larry

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diff --git a/drivers/net/wireless/realtek/rtw88/main.c b/drivers/net/wireless/realtek/rtw88/main.c
index a189c4500fd9..690c0a68a038 100644
--- a/drivers/net/wireless/realtek/rtw88/main.c
+++ b/drivers/net/wireless/realtek/rtw88/main.c
@@ -902,6 +902,7 @@ static int rtw_chip_efuse_enable(struct rtw_dev *rtwdev)
 		goto err;
 	}
 
+	wait_for_completion(&fw->completion);
 	rtw_write8(rtwdev, REG_C2HEVT, C2H_HW_FEATURE_DUMP);
 	ret = rtw_download_firmware(rtwdev, fw->firmware->data,
 				    fw->firmware->size);

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