RE: [bug report] rtw89: add Realtek 802.11ax driver

[Pkshih <pkshih@realtek.com>]

> -----Original Message-----
> From: Dan Carpenter <dan.carpenter@oracle.com>
> Sent: Monday, November 8, 2021 10:47 PM
> To: Pkshih <pkshih@realtek.com>
> Cc: linux-wireless@vger.kernel.org
> Subject: [bug report] rtw89: add Realtek 802.11ax driver
> 
> Hello Ping-Ke Shih,
> 
> The patch e3ec7017f6a2: "rtw89: add Realtek 802.11ax driver" from Oct
> 11, 2021, leads to the following Smatch static checker warning:
> 
> 	drivers/net/wireless/realtek/rtw89/mac.c:586 hfc_ch_ctrl()
> 	warn: array off by one? 'cfg[ch]'
> 
> drivers/net/wireless/realtek/rtw89/mac.c
>     568 static int hfc_ch_ctrl(struct rtw89_dev *rtwdev, u8 ch)
>     569 {
>     570         struct rtw89_hfc_param *param = &rtwdev->mac.hfc_param;
>     571         const struct rtw89_hfc_ch_cfg *cfg = param->ch_cfg;
>     572         int ret = 0;
>     573         u32 val = 0;
>     574
>     575         ret = rtw89_mac_check_mac_en(rtwdev, RTW89_MAC_0, RTW89_DMAC_SEL);
>     576         if (ret)
>     577                 return ret;
>     578
>     579         ret = hfc_ch_cfg_chk(rtwdev, ch);
>     580         if (ret)
>     581                 return ret;
>     582
>     583         if (ch > RTW89_DMA_B1HI)
>                     ^^^^^^^^^^^^^^^^^^^
> 
>     584                 return -EINVAL;
>     585
> --> 586         val = u32_encode_bits(cfg[ch].min, B_AX_MIN_PG_MASK) |
>     587               u32_encode_bits(cfg[ch].max, B_AX_MAX_PG_MASK) |
>     588               (cfg[ch].grp ? B_AX_GRP : 0);
> 
> This is an unpublished Smatch warning which uses an "assume every >
> comparison should be >= wrong until proven otherwise" approach.  In
> this case, Smatch can't tell the size of the cfg[] array.

I'm not clear how to fix this warning. Any suggestion?

The caller of this function is
	for (ch = RTW89_DMA_ACH0; ch < RTW89_DMA_H2C; ch++) {
		ret = hfc_ch_ctrl(rtwdev, ch);
		...
	}

So, 'ch' is between 0 and 11. Maybe, this checking can be removed?

> 
> Manually it looks like cfg can only be rtw8852a_hfc_chcfg_pcie[] which
> has RTW89_DMA_CH_NUM (13) elements.  Is there a reason why we don't use
> the last element?  

We don't use the last element, because channel 0 to 11 are the regular TX channels
that will transmit packets to air. The channel 12 (H2C) is a special channel we
send firmware commands from driver, so it doesn't need additional configurations.
More, the list of R_AX_ACH0_PAGE_CTRL series don't have one for channel 12 neither.

> Also it's puzzling that the last element is
> FWCMDQ instead of H2C.  So maybe that's the reason?

FWCMDQ is a queue or channel that is used to send H2C from driver to firmware.
So, FWCMD and H2C can be seen as synonyms, as well as FWCMDQ and H2CQ.

> 
>     589         rtw89_write32(rtwdev, R_AX_ACH0_PAGE_CTRL + ch * 4, val);
>     590
>     591         return 0;
>     592 }
> 

--
Ping-Ke