linux-kernel - Re: [PATCH v1] mt76: mt7615: Fix build with older compilers

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Message-ID: <0101016ec5ed7c43-209a11a1-70b1-4151-bf9c-a2c5ce9f5348-000000@us-west-2.amazonses.com>
Date:   Mon, 2 Dec 2019 09:25:05 +0000
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Pablo Greco <pgreco@...tosproject.org>
Cc:     Felix Fietkau <nbd@....name>,
        Lorenzo Bianconi <lorenzo.bianconi83@...il.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Roy Luo <royluo@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mt76: mt7615: Fix build with older compilers

Pablo Greco <pgreco@...tosproject.org> writes:

> Some compilers (tested with 4.8.5 from CentOS 7) fail properly process
> FIELD_GET inside an inline function, which ends up in a BUILD_BUG_ON.
> Convert inline function to a macro.
>
> Fixes commit bf92e7685100 ("mt76: mt7615: add support for per-chain
> signal strength reporting")
> Reported in https://lkml.org/lkml/2019/9/21/146
>
> Reported-by: kbuild test robot <lkp@...el.com>
> Signed-off-by: Pablo Greco <pgreco@...tosproject.org>
> ---
>  drivers/net/wireless/mediatek/mt76/mt7615/mac.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7615/mac.c b/drivers/net/wireless/mediatek/mt76/mt7615/mac.c
> index c77adc5d2552..77e395ca2c6a 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt7615/mac.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt7615/mac.c
> @@ -13,10 +13,7 @@
>  #include "../dma.h"
>  #include "mac.h"
>  
> -static inline s8 to_rssi(u32 field, u32 rxv)
> -{
> -	return (FIELD_GET(field, rxv) - 220) / 2;
> -}
> +#define to_rssi(field, rxv)		((FIELD_GET(field, rxv) - 220) / 2)

What about u32_get_bits() instead of FIELD_GET(), would that work? I
guess chances for that is slim, but it's always a shame to convert a
function to a macro so we should try other methods first.

Or even better if we could fix FIELD_GET() to work with older compilers.

-- 
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches