netdev - Re: [PATCH net] gve: DQO: Suppress unused var warnings

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Date:   Mon, 27 Sep 2021 16:59:44 -0700
From:   Bailey Forrest <bcf@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH net] gve: DQO: Suppress unused var warnings

On Mon, Sep 27, 2021 at 4:21 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 27 Sep 2021 13:21:30 -0700 Bailey Forrest wrote:
> > Apologies, resending as text
> >
> > On Mon, Sep 27, 2021 at 2:59 AM Arnd Bergmann <arnd@...nel.org> wrote:
> > >
> > > On Sat, Jul 24, 2021 at 1:19 AM Bailey Forrest <bcf@...gle.com> wrote:
> > > >
> > > > Some variables become unused when `CONFIG_NEED_DMA_MAP_STATE=n`.
> > > >
> > > > We only suppress when `CONFIG_NEED_DMA_MAP_STATE=n` in order to avoid
> > > > false negatives.
> > > >
> > > > Fixes: a57e5de476be ("gve: DQO: Add TX path")
> > > > Signed-off-by: Bailey Forrest <bcf@...gle.com>
> > >
> > > Hi Bailey,
> > >
> > > I see that the warning still exists in linux-5.15-rc3 and net-next,
> > > I'm building with my original patch[1] to get around the -Werror
> > > warnings.
> > >
> > > Can you resend your patch, or should I resend mine after all?
> > >
> > >       Arnd
> > >
> > > [1] https://lore.kernel.org/all/20210721151100.2042139-1-arnd@kernel.org/
> >
> > Hi David/Jakub,
> >
> > Any thoughts on my patch? I'm open to alternative suggestions for how
> > to resolve this.
> >
> > This patch still works and merges cleanly on HEAD.
>
> Looks like fixing this on the wrong end, dma_unmap_len_set()
> and friends should always evaluate their arguments.

That makes sense.

Arnd, if you want to fix this inside of the dma_* macros, the
following diff resolves the errors reported for this driver:

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index dca2b1355bb1..f51eee0f678e 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -590,10 +590,21 @@ static inline int dma_mmap_wc(struct device *dev,
 #else
 #define DEFINE_DMA_UNMAP_ADDR(ADDR_NAME)
 #define DEFINE_DMA_UNMAP_LEN(LEN_NAME)
-#define dma_unmap_addr(PTR, ADDR_NAME)           (0)
-#define dma_unmap_addr_set(PTR, ADDR_NAME, VAL)  do { } while (0)
-#define dma_unmap_len(PTR, LEN_NAME)             (0)
-#define dma_unmap_len_set(PTR, LEN_NAME, VAL)    do { } while (0)
+
+#define dma_unmap_addr(PTR, ADDR_NAME) ({ (void)PTR; 0; })
+
+#define dma_unmap_addr_set(PTR, ADDR_NAME, VAL) do { \
+ (void)PTR; \
+ (void)VAL; \
+} while (0)
+
+#define dma_unmap_len(PTR, LEN_NAME) ({ (void)PTR; 0; })
+
+#define dma_unmap_len_set(PTR, LEN_NAME, VAL) do { \
+ (void)PTR; \
+ (void)VAL; \
+} while (0)
+
 #endif

 #endif /* _LINUX_DMA_MAPPING_H */