A new warning in clang points out two instances where boolean
expressions are being used with a bitwise OR instead of logical OR:
drivers/soc/tegra/fuse/speedo-tegra20.c:72:9: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
reg = tegra_fuse_read_spare(i) |
^~~~~~~~~~~~~~~~~~~~~~~~~~
||
drivers/soc/tegra/fuse/speedo-tegra20.c:72:9: note: cast one or both operands to int to silence this warning
drivers/soc/tegra/fuse/speedo-tegra20.c:87:9: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
reg = tegra_fuse_read_spare(i) |
^~~~~~~~~~~~~~~~~~~~~~~~~~
||
drivers/soc/tegra/fuse/speedo-tegra20.c:87:9: note: cast one or both operands to int to silence this warning
2 warnings generated.
The motivation for the warning is that logical operations short circuit
while bitwise operations do not. In this case, it does not seem like
short circuiting is harmful so implement the suggested fix of changing
to a logical operation to fix the warning.
Link: https://github.com/ClangBuiltLinux/linux/issues/1488
Signed-off-by: Nathan Chancellor <[email protected]>
---
drivers/soc/tegra/fuse/speedo-tegra20.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/soc/tegra/fuse/speedo-tegra20.c b/drivers/soc/tegra/fuse/speedo-tegra20.c
index 2546bddbab93..4984246605ae 100644
--- a/drivers/soc/tegra/fuse/speedo-tegra20.c
+++ b/drivers/soc/tegra/fuse/speedo-tegra20.c
@@ -69,7 +69,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
val = 0;
for (i = CPU_SPEEDO_MSBIT; i >= CPU_SPEEDO_LSBIT; i--) {
- reg = tegra_fuse_read_spare(i) |
+ reg = tegra_fuse_read_spare(i) ||
tegra_fuse_read_spare(i + CPU_SPEEDO_REDUND_OFFS);
val = (val << 1) | (reg & 0x1);
}
@@ -84,7 +84,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
val = 0;
for (i = SOC_SPEEDO_MSBIT; i >= SOC_SPEEDO_LSBIT; i--) {
- reg = tegra_fuse_read_spare(i) |
+ reg = tegra_fuse_read_spare(i) ||
tegra_fuse_read_spare(i + SOC_SPEEDO_REDUND_OFFS);
val = (val << 1) | (reg & 0x1);
}
base-commit: 519d81956ee277b4419c723adfb154603c2565ba
--
2.33.1.637.gf443b226ca
On Thu, Oct 21, 2021 at 02:45:00PM -0700, Nathan Chancellor wrote:
[...]
> --- a/drivers/soc/tegra/fuse/speedo-tegra20.c
> +++ b/drivers/soc/tegra/fuse/speedo-tegra20.c
> @@ -69,7 +69,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
>
> val = 0;
> for (i = CPU_SPEEDO_MSBIT; i >= CPU_SPEEDO_LSBIT; i--) {
> - reg = tegra_fuse_read_spare(i) |
> + reg = tegra_fuse_read_spare(i) ||
> tegra_fuse_read_spare(i + CPU_SPEEDO_REDUND_OFFS);
> val = (val << 1) | (reg & 0x1);
> }
> @@ -84,7 +84,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
>
> val = 0;
> for (i = SOC_SPEEDO_MSBIT; i >= SOC_SPEEDO_LSBIT; i--) {
> - reg = tegra_fuse_read_spare(i) |
> + reg = tegra_fuse_read_spare(i) ||
> tegra_fuse_read_spare(i + SOC_SPEEDO_REDUND_OFFS);
> val = (val << 1) | (reg & 0x1);
> }
It does seem correct, but nevertheless the code looks suspicious. reg is
already masked with 0x1 as far as I can tell, and there are other places
which depend on this (like speedo-tegra210.c). Guessing from the use of
tegra_fuse_read_spare() I would recommend changing its return type as it
is returing a bit value, not necessarily semantically a boolean.
Best Regards
Micha? Miros?aw
Hi Michał,
On Thu, Oct 21, 2021 at 11:55:34PM +0200, Michał Mirosław wrote:
> On Thu, Oct 21, 2021 at 02:45:00PM -0700, Nathan Chancellor wrote:
> [...]
> > --- a/drivers/soc/tegra/fuse/speedo-tegra20.c
> > +++ b/drivers/soc/tegra/fuse/speedo-tegra20.c
> > @@ -69,7 +69,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
> >
> > val = 0;
> > for (i = CPU_SPEEDO_MSBIT; i >= CPU_SPEEDO_LSBIT; i--) {
> > - reg = tegra_fuse_read_spare(i) |
> > + reg = tegra_fuse_read_spare(i) ||
> > tegra_fuse_read_spare(i + CPU_SPEEDO_REDUND_OFFS);
> > val = (val << 1) | (reg & 0x1);
> > }
> > @@ -84,7 +84,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
> >
> > val = 0;
> > for (i = SOC_SPEEDO_MSBIT; i >= SOC_SPEEDO_LSBIT; i--) {
> > - reg = tegra_fuse_read_spare(i) |
> > + reg = tegra_fuse_read_spare(i) ||
> > tegra_fuse_read_spare(i + SOC_SPEEDO_REDUND_OFFS);
> > val = (val << 1) | (reg & 0x1);
> > }
>
> It does seem correct, but nevertheless the code looks suspicious. reg is
> already masked with 0x1 as far as I can tell, and there are other places
> which depend on this (like speedo-tegra210.c). Guessing from the use of
> tegra_fuse_read_spare() I would recommend changing its return type as it
> is returing a bit value, not necessarily semantically a boolean.
Yes, I did notice that, as well as the use of tegra_fuse_read_spare()
with boolean operators in tegra-apbmisc.c. I could change it to int if
that is what the maintainers prefer, which would also solve the warning.
Cheers,
Nathan
+ Anders (combining
https://lore.kernel.org/all/[email protected]/).
On Thu, Oct 21, 2021 at 2:45 PM Nathan Chancellor <[email protected]> wrote:
>
> A new warning in clang points out two instances where boolean
> expressions are being used with a bitwise OR instead of logical OR:
>
> drivers/soc/tegra/fuse/speedo-tegra20.c:72:9: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
> reg = tegra_fuse_read_spare(i) |
> ^~~~~~~~~~~~~~~~~~~~~~~~~~
> ||
> drivers/soc/tegra/fuse/speedo-tegra20.c:72:9: note: cast one or both operands to int to silence this warning
> drivers/soc/tegra/fuse/speedo-tegra20.c:87:9: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
> reg = tegra_fuse_read_spare(i) |
> ^~~~~~~~~~~~~~~~~~~~~~~~~~
> ||
> drivers/soc/tegra/fuse/speedo-tegra20.c:87:9: note: cast one or both operands to int to silence this warning
> 2 warnings generated.
>
> The motivation for the warning is that logical operations short circuit
> while bitwise operations do not. In this case, it does not seem like
> short circuiting is harmful so implement the suggested fix of changing
> to a logical operation to fix the warning.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1488
> Signed-off-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Fixes: 25cd5a391478 ("ARM: tegra: Add speedo-based process identification")
> ---
> drivers/soc/tegra/fuse/speedo-tegra20.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/soc/tegra/fuse/speedo-tegra20.c b/drivers/soc/tegra/fuse/speedo-tegra20.c
> index 2546bddbab93..4984246605ae 100644
> --- a/drivers/soc/tegra/fuse/speedo-tegra20.c
> +++ b/drivers/soc/tegra/fuse/speedo-tegra20.c
> @@ -69,7 +69,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
>
> val = 0;
> for (i = CPU_SPEEDO_MSBIT; i >= CPU_SPEEDO_LSBIT; i--) {
> - reg = tegra_fuse_read_spare(i) |
> + reg = tegra_fuse_read_spare(i) ||
> tegra_fuse_read_spare(i + CPU_SPEEDO_REDUND_OFFS);
> val = (val << 1) | (reg & 0x1);
> }
> @@ -84,7 +84,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
>
> val = 0;
> for (i = SOC_SPEEDO_MSBIT; i >= SOC_SPEEDO_LSBIT; i--) {
> - reg = tegra_fuse_read_spare(i) |
> + reg = tegra_fuse_read_spare(i) ||
> tegra_fuse_read_spare(i + SOC_SPEEDO_REDUND_OFFS);
> val = (val << 1) | (reg & 0x1);
> }
>
> base-commit: 519d81956ee277b4419c723adfb154603c2565ba
> --
> 2.33.1.637.gf443b226ca
>
--
Thanks,
~Nick Desaulniers