Re: drivers/clk/clk-k210.c:717:6: warning: variable 'reg' set but not used

From: Palmer Dabbelt
Date: Fri Jun 11 2021 - 23:56:03 EST

On Thu, 03 Jun 2021 03:03:14 PDT (-0700), Damien Le Moal wrote:
On 2021/06/03 18:35, kernel test robot wrote:
tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head: 324c92e5e0ee0e993bdb106fac407846ed677f6b
commit: c6ca7616f7d5c2ce166280107ba74db1d528fcb7 clk: Add RISC-V Canaan Kendryte K210 clock driver
date: 3 months ago
config: riscv-randconfig-r033-20210603 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project d8e0ae9a76a62bdc6117630d59bf9967ac9bb4ea)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# install riscv cross compiling tool for clang build
# apt-get install binutils-riscv64-linux-gnu
# https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c6ca7616f7d5c2ce166280107ba74db1d528fcb7
git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git fetch --no-tags linus master
git checkout c6ca7616f7d5c2ce166280107ba74db1d528fcb7
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=riscv
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All warnings (new ones prefixed by >>):

In file included from drivers/clk/clk-k210.c:8:
In file included from include/linux/io.h:13:
In file included from arch/riscv/include/asm/io.h:149:
include/asm-generic/io.h:556:9: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return inb(addr);
^~~~~~~~~
arch/riscv/include/asm/io.h:55:76: note: expanded from macro 'inb'
#define inb(c) ({ u8 __v; __io_pbr(); __v = readb_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
~~~~~~~~~~ ^
arch/riscv/include/asm/mmio.h:87:48: note: expanded from macro 'readb_cpu'
#define readb_cpu(c) ({ u8 __r = __raw_readb(c); __r; })
^
In file included from drivers/clk/clk-k210.c:8:
In file included from include/linux/io.h:13:
In file included from arch/riscv/include/asm/io.h:149:
include/asm-generic/io.h:564:9: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return inw(addr);
^~~~~~~~~
arch/riscv/include/asm/io.h:56:76: note: expanded from macro 'inw'
#define inw(c) ({ u16 __v; __io_pbr(); __v = readw_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
~~~~~~~~~~ ^
arch/riscv/include/asm/mmio.h:88:76: note: expanded from macro 'readw_cpu'
#define readw_cpu(c) ({ u16 __r = le16_to_cpu((__force __le16)__raw_readw(c)); __r; })
^
include/uapi/linux/byteorder/little_endian.h:36:51: note: expanded from macro '__le16_to_cpu'
#define __le16_to_cpu(x) ((__force __u16)(__le16)(x))
^
In file included from drivers/clk/clk-k210.c:8:
In file included from include/linux/io.h:13:
In file included from arch/riscv/include/asm/io.h:149:
include/asm-generic/io.h:572:9: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return inl(addr);
^~~~~~~~~
arch/riscv/include/asm/io.h:57:76: note: expanded from macro 'inl'
#define inl(c) ({ u32 __v; __io_pbr(); __v = readl_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
~~~~~~~~~~ ^
arch/riscv/include/asm/mmio.h:89:76: note: expanded from macro 'readl_cpu'
#define readl_cpu(c) ({ u32 __r = le32_to_cpu((__force __le32)__raw_readl(c)); __r; })
^
include/uapi/linux/byteorder/little_endian.h:34:51: note: expanded from macro '__le32_to_cpu'
#define __le32_to_cpu(x) ((__force __u32)(__le32)(x))
^
In file included from drivers/clk/clk-k210.c:8:
In file included from include/linux/io.h:13:
In file included from arch/riscv/include/asm/io.h:149:
include/asm-generic/io.h:580:2: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
outb(value, addr);
^~~~~~~~~~~~~~~~~
arch/riscv/include/asm/io.h:59:68: note: expanded from macro 'outb'
#define outb(v,c) ({ __io_pbw(); writeb_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
~~~~~~~~~~ ^
arch/riscv/include/asm/mmio.h:91:52: note: expanded from macro 'writeb_cpu'
#define writeb_cpu(v, c) ((void)__raw_writeb((v), (c)))
^
In file included from drivers/clk/clk-k210.c:8:
In file included from include/linux/io.h:13:
In file included from arch/riscv/include/asm/io.h:149:
include/asm-generic/io.h:588:2: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
outw(value, addr);
^~~~~~~~~~~~~~~~~
arch/riscv/include/asm/io.h:60:68: note: expanded from macro 'outw'
#define outw(v,c) ({ __io_pbw(); writew_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
~~~~~~~~~~ ^
arch/riscv/include/asm/mmio.h:92:76: note: expanded from macro 'writew_cpu'
#define writew_cpu(v, c) ((void)__raw_writew((__force u16)cpu_to_le16(v), (c)))
^
In file included from drivers/clk/clk-k210.c:8:
In file included from include/linux/io.h:13:
In file included from arch/riscv/include/asm/io.h:149:
include/asm-generic/io.h:596:2: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
outl(value, addr);
^~~~~~~~~~~~~~~~~
arch/riscv/include/asm/io.h:61:68: note: expanded from macro 'outl'
#define outl(v,c) ({ __io_pbw(); writel_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
~~~~~~~~~~ ^
arch/riscv/include/asm/mmio.h:93:76: note: expanded from macro 'writel_cpu'
#define writel_cpu(v, c) ((void)__raw_writel((__force u32)cpu_to_le32(v), (c)))
^
In file included from drivers/clk/clk-k210.c:8:
In file included from include/linux/io.h:13:
In file included from arch/riscv/include/asm/io.h:149:
include/asm-generic/io.h:1005:55: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return (port > MMIO_UPPER_LIMIT) ? NULL : PCI_IOBASE + port;
~~~~~~~~~~ ^
drivers/clk/clk-k210.c:717:6: warning: variable 'reg' set but not used [-Wunused-but-set-variable]
u32 reg;
^
8 warnings generated.


vim +/reg +717 drivers/clk/clk-k210.c

710
711 static int k210_clk_set_parent(struct clk_hw *hw, u8 index)
712 {
713 struct k210_clk *kclk = to_k210_clk(hw);
714 struct k210_sysclk *ksc = kclk->ksc;
715 struct k210_clk_cfg *cfg = &k210_clk_cfgs[kclk->id];
716 unsigned long flags;
> 717 u32 reg;

Palmer,

I do not think this driver is the real cause of this error. Did something change
recently with risc-v mmio readl()/writel() ?

I have no idea what's going on here. When I try to re-build that config I don't get any warnings or errors. That said...

718
719 spin_lock_irqsave(&ksc->clk_lock, flags);
720 reg = readl(ksc->regs + cfg->mux_reg);
721 if (index)
722 reg |= BIT(cfg->mux_bit);
723 else
724 reg &= ~BIT(cfg->mux_bit);
725 spin_unlock_irqrestore(&ksc->clk_lock, flags);

Isn't reg unused here? That's one of the warnings.

The void* casting has been there for a while and looks like a real bug, but asm-generic adopted our {in,out}{bwlq} implementation so I'm just going to toss ours. I'm not quite sure why the generic ones aren't doing arithmetic on void*, but I'm not getting warnings.

726
727 return 0;
728 }
729

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx



--
Damien Le Moal
Western Digital Research