| Message ID | 4391788.dtYArQ4mVi@wuerfel (mailing list archive) |
|---|---|
| State | New, archived |
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From: Arnd Bergmann <arnd@arndb.de> Date: Thu, 12 Nov 2015 15:12:48 +0100 > Building dwmac-ipq806x on a 64-bit architecture produces a harmless > warning from gcc: > > stmmac/dwmac-ipq806x.c: In function 'ipq806x_gmac_probe': > include/linux/bitops.h:6:19: warning: overflow in implicit constant conversion [-Woverflow] > val = QSGMII_PHY_CDR_EN | > stmmac/dwmac-ipq806x.c:333:8: note: in expansion of macro 'QSGMII_PHY_CDR_EN' > #define QSGMII_PHY_CDR_EN BIT(0) > #define BIT(nr) (1UL << (nr)) > > The compiler warns about the fact that a 64-bit literal is passed > into a function that takes a 32-bit argument. I could not fully understand > why it warns despite the fact that this number is always small enough > to fit, but changing the use of BIT() macros into the equivalent hexadecimal > representation avoids the warning > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > Fixes: b1c17215d718 ("stmmac: add ipq806x glue layer") I've seen this warning too on x86_64 and had been meaning to look into it, thanks for taking the initiative. :) Moving away from using BIT() is somewhat disappointing, because we want to encourage people to use these macros. I think it's also easier from a driver author and auditing perspective, you can see that something is being defined as bit X and then check the documentation for the chip to see if bit X is correct or not. With the hex values there is more mental work and room for... mistakes. Also I don't even understand the compiler's behavior, it's warning about QSGMII_PHY_CDR_EN but if you define only that to "0x1u" it still warns about QSGMII_PHY_CDR_EN. The warning goes away only if you change all 5 BIT() uses. This makes me like the change even less, something foul is going on here and I'd rather figure out what that is than install this patch. Thanks.
On Thursday 12 November 2015 12:25:28 David Miller wrote: > From: Arnd Bergmann <arnd@arndb.de> > Date: Thu, 12 Nov 2015 15:12:48 +0100 > > > Building dwmac-ipq806x on a 64-bit architecture produces a harmless > > warning from gcc: > > > > stmmac/dwmac-ipq806x.c: In function 'ipq806x_gmac_probe': > > include/linux/bitops.h:6:19: warning: overflow in implicit constant conversion [-Woverflow] > > val = QSGMII_PHY_CDR_EN | > > stmmac/dwmac-ipq806x.c:333:8: note: in expansion of macro 'QSGMII_PHY_CDR_EN' > > #define QSGMII_PHY_CDR_EN BIT(0) > > #define BIT(nr) (1UL << (nr)) > > > > The compiler warns about the fact that a 64-bit literal is passed > > into a function that takes a 32-bit argument. I could not fully understand > > why it warns despite the fact that this number is always small enough > > to fit, but changing the use of BIT() macros into the equivalent hexadecimal > > representation avoids the warning > > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > Fixes: b1c17215d718 ("stmmac: add ipq806x glue layer") > > I've seen this warning too on x86_64 and had been meaning to look > into it, thanks for taking the initiative. > > Moving away from using BIT() is somewhat disappointing, because we > want to encourage people to use these macros. Ok, I never really liked that macro, so I didn't mind removing it. ;-) I spent too much time working at IBM where all internal documentation uses bit numbers that call the MSB bit 0, and drivers use randomly either the IBM notation or the one that everyone else uses, so I always found the hex numbers way more intuitive. > Also I don't even understand the compiler's behavior, it's warning > about QSGMII_PHY_CDR_EN but if you define only that to "0x1u" it still > warns about QSGMII_PHY_CDR_EN. > > The warning goes away only if you change all 5 BIT() uses. Yes, I have spent the time to analyze the problem now and it all makes sense. A proper patch follows. Arnd
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c index 9d89bdbf029f..4abd9b0b542a 100644 --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c @@ -77,11 +77,11 @@ /* Only GMAC1/2/3 support SGMII and their CTL register are not contiguous */ #define QSGMII_PHY_SGMII_CTL(x) ((x == 1) ? 0x134 : \ (0x13c + (4 * (x - 2)))) -#define QSGMII_PHY_CDR_EN BIT(0) -#define QSGMII_PHY_RX_FRONT_EN BIT(1) -#define QSGMII_PHY_RX_SIGNAL_DETECT_EN BIT(2) -#define QSGMII_PHY_TX_DRIVER_EN BIT(3) -#define QSGMII_PHY_QSGMII_EN BIT(7) +#define QSGMII_PHY_CDR_EN 0x01u +#define QSGMII_PHY_RX_FRONT_EN 0x02u +#define QSGMII_PHY_RX_SIGNAL_DETECT_EN 0x04u +#define QSGMII_PHY_TX_DRIVER_EN 0x08u +#define QSGMII_PHY_QSGMII_EN 0x80u #define QSGMII_PHY_PHASE_LOOP_GAIN_OFFSET 12 #define QSGMII_PHY_PHASE_LOOP_GAIN_MASK 0x7 #define QSGMII_PHY_RX_DC_BIAS_OFFSET 18
Building dwmac-ipq806x on a 64-bit architecture produces a harmless warning from gcc: stmmac/dwmac-ipq806x.c: In function 'ipq806x_gmac_probe': include/linux/bitops.h:6:19: warning: overflow in implicit constant conversion [-Woverflow] val = QSGMII_PHY_CDR_EN | stmmac/dwmac-ipq806x.c:333:8: note: in expansion of macro 'QSGMII_PHY_CDR_EN' #define QSGMII_PHY_CDR_EN BIT(0) #define BIT(nr) (1UL << (nr)) The compiler warns about the fact that a 64-bit literal is passed into a function that takes a 32-bit argument. I could not fully understand why it warns despite the fact that this number is always small enough to fit, but changing the use of BIT() macros into the equivalent hexadecimal representation avoids the warning Signed-off-by: Arnd Bergmann <arnd@arndb.de> Fixes: b1c17215d718 ("stmmac: add ipq806x glue layer") --- This came up on the arm64 allmodconfig build