-Wconstant-conversion in drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c

-Wconstant-conversion in drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c

[Nathan Chancellor]

Hi Arend,

After [1] landed in clang main, I am seeing the following warning
(turned error with CONFIG_WERROR=y / W=e):

  drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:224:18: error: implicit conversion from 'int' to 's8' (aka 'signed char') changes value from 128 to -128 [-Werror,-Wconstant-conversion]
    224 |         {0, 0, 0, 0, 0, 128},
        |         ~               ^~~

As far as I can tell, this has been present since the original commit
that added brcm80211 to the tree

  a9533e7ea3c4 ("Staging: Add initial release of brcm80211 - Broadcom 802.11n wireless LAN driver.")

based on my reading of drivers/staging/brcm80211/phy/wlc_phy_n.c. Should
this final value be changed to -128 or should there be some other fix?

[1]: https://github.com/llvm/llvm-project/commit/a5ef934a8d295dc03be3960f2b3744ec2e53238e

-- 
Cheers,
Nathan

Re: -Wconstant-conversion in drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c

[Arend van Spriel]

resending...


Op 16 september 2026 08:45:59 schreef Nathan Chancellor <nathan@kernel.org>:

> Hi Arend,
>
> After [1] landed in clang main, I am seeing the following warning
> (turned error with CONFIG_WERROR=y / W=e):
>
> drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:224:18: error: 
> implicit conversion from 'int' to 's8' (aka 'signed char') changes value 
> from 128 to -128 [-Werror,-Wconstant-conversion]
> 224 |         {0, 0, 0, 0, 0, 128},
> |         ~               ^~~
>
> As far as I can tell, this has been present since the original commit
> that added brcm80211 to the tree
>
> a9533e7ea3c4 ("Staging: Add initial release of brcm80211 - Broadcom 802.11n 
> wireless LAN driver.")
>
> based on my reading of drivers/staging/brcm80211/phy/wlc_phy_n.c. Should
> this final value be changed to -128 or should there be some other fix?

To be honest I don't know. If I looked at the proprietary driver code that 
table entry is still there with exactly the same values. So to be type 
correct while preserving the same value it should be -128. However, looking 
at the table entry struct it is an index so that sounds odd.

Regards,
Arend

Re: -Wconstant-conversion in drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c

[Nathan Chancellor]

On Sun, Oct 04, 2026 at 07:07:01PM +0200, Arend van Spriel wrote:
> Op 16 september 2026 08:45:59 schreef Nathan Chancellor <nathan@kernel.org>:
> 
> > Hi Arend,
> > 
> > After [1] landed in clang main, I am seeing the following warning
> > (turned error with CONFIG_WERROR=y / W=e):
> > 
> > drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:224:18:
> > error: implicit conversion from 'int' to 's8' (aka 'signed char')
> > changes value from 128 to -128 [-Werror,-Wconstant-conversion]
> > 224 |         {0, 0, 0, 0, 0, 128},
> > |         ~               ^~~
> > 
> > As far as I can tell, this has been present since the original commit
> > that added brcm80211 to the tree
> > 
> > a9533e7ea3c4 ("Staging: Add initial release of brcm80211 - Broadcom
> > 802.11n wireless LAN driver.")
> > 
> > based on my reading of drivers/staging/brcm80211/phy/wlc_phy_n.c. Should
> > this final value be changed to -128 or should there be some other fix?
> 
> To be honest I don't know. If I looked at the proprietary driver code that
> table entry is still there with exactly the same values. So to be type
> correct while preserving the same value it should be -128. However, looking
> at the table entry struct it is an index so that sounds odd.

Thanks a lot for the input! I sent a patch to change it to -128 to clear
up the warning since it will be the same bit representation and
presumably things are working properly with that:

  https://lore.kernel.org/20260916064454.GA3635613@ax162/

-- 
Cheers,
Nathan