Hi Dan,
On Mon, Oct 19, 2015 at 05:10 PM CEST, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> The patch a619d1abe20c: "rtlwifi: rtl8723be: Add new driver" from Feb
> 28, 2014, leads to the following static checker warning:
>
> drivers/net/wireless/realtek/rtlwifi/rtl8723be/hw.c:1802 _rtl8723be_read_power_value_fromprom()
> warn: why is the last element skipped?
>
> drivers/net/wireless/realtek/rtlwifi/rtl8723be/hw.c
[snip]
> 1794 for (path = 0; path < MAX_RF_PATH; path++) {
> 1795 /*2.4G default value*/
> 1796 for (group = 0; group < MAX_CHNL_GROUP_24G; group++) {
> ^^^^^^^^^^^^^^^^^^^^^^^^^^
> Here we go to the end.
>
> 1797 pw2g->index_cck_base[path][group] = hwinfo[addr++];
> 1798 if (pw2g->index_cck_base[path][group] == 0xFF)
> 1799 pw2g->index_cck_base[path][group] = 0x2D;
> 1800
> 1801 }
> 1802 for (group = 0; group < MAX_CHNL_GROUP_24G - 1; group++) {
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Here we skip the last element. So far as I can see this looks like a
> mistake but I don't know the code well.
>
> 1803 pw2g->index_bw40_base[path][group] = hwinfo[addr++];
> 1804 if (pw2g->index_bw40_base[path][group] == 0xFF)
> 1805 pw2g->index_bw40_base[path][group] = 0x2D;
> 1806 }
I have seen the same thing in rtlwifi/rtl8188ee and staging/rtl8188eu
drivers (see read_power_value_fromprom() and
Hal_ReadPowerValueFromPROM_8188E(), respectively), and I've asked myself
exactly the same question before so I'll share my thoughts.
Please take it all with a grain of salt, I'm new at this.
The rtl8188e[eu] drivers divide 2.4 GHz channels into six sets
(MAX_CHNL_GROUP_24G == 6) as far as the TX power goes (see
_rtl88e_get_chnl_group(), Hal_GetChnlGroup88E()):
group 0: 1-2
group 1: 3-5
group 2: 6-8
group 3: 9-11
group 4: 12-13
group 5: 14
As you see the last group is special, it's only channel 14, which
applies only to 802.11b in Japan, AFAIK. The loop in question
initializes the index_bw40_base[] array, which name suggests that it is
related to 40 MHz channel bandwidth - 802.11n only then. That would
explain the `MAX_CHNL_GROUP_24G - 1' expression.
This is the case for rtl8188e[eu]. However, rtl8723be driver divides
2.4 GHz channels into just three groups - 0: 1-3, 1: 4-9, and 2: 10-14
(_rtl8723be_get_chnl_group()). In that regard it is similar to
rtlwifi/rtl8192cu and staging/rtl8723au (rtl92c_get_chnl_group(),
Hal_GetChnlGroup()).
That would mean that the index_bw40_base[3..5] range in this
one-size-fits all array is never accessed by the rtl8723be driver.
That's all I know, beyond that point I tell myself that it's a driver
for a chip with no datasheet so questions without answers are part of
the deal ;-)
Cheers,
Jakub
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