Re: [PATCH V5 2/5] PCI/TPH: Add Steering Tag support

Wei Huang
2024-09-17T14:31:09Z

On 9/17/24 02:32, Simon Horman wrote:
> On Mon, Sep 16, 2024 at 03:51:00PM -0500, Wei Huang wrote:
...
>> + val = readl(vec_ctrl);
>> + mask = PCI_MSIX_ENTRY_CTRL_ST_LOWER | PCI_MSIX_ENTRY_CTRL_ST_UPPER;
>> + val &= ~mask;
>> + val |= FIELD_PREP(mask, (u32)tag);
>
> Hi Wei Huang,
>
> Unfortunately clang-18 (x86_64, allmodconfig, W=1, when applied to net-next)
> complains about this. I think it is because it expects FIELD_PREP to be
> used with a mask that is a built-in constant.

I thought I fixed it, but apparently not enough for clang-18. I will
address this problem, along with other comments from you and Bjorn (if any).

BTW there is another code in drivers/gpu/drm/ using a similar approach.

>
> drivers/pci/pcie/tph.c:232:9: warning: result of comparison of constant 18446744073709551615 with expression of type 'typeof (_Generic((mask), char: (unsigned char)0, unsigned char: (unsigned char)0, signed char: (unsigned char)0, unsigned short: (unsigned short)0, short: (unsigned short)0, unsigned int: (unsigned int)0, int: (unsigned int)0, unsigned long: (unsigned long)0, long: (unsigned long)0, unsigned long long: (unsigned long long)0, long long: (unsigned long long)0, default: (mask)))' (aka 'unsigned int') is always false [-Wtautological-constant-out-of-range-compare]
> 232 | val |= FIELD_PREP(mask, (u32)tag);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/bitfield.h:115:3: note: expanded from macro 'FIELD_PREP'
> 115 | __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/bitfield.h:72:53: note: expanded from macro '__BF_FIELD_CHECK'
> 72 | BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \
> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
> 73 | __bf_cast_unsigned(_reg, ~0ull), \
> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 74 | _pfx "type of reg too small for mask"); \
> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/build_bug.h:39:58: note: expanded from macro 'BUILD_BUG_ON_MSG'
> 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
> ././include/linux/compiler_types.h:510:22: note: expanded from macro 'compiletime_assert'
> 510 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> | ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ././include/linux/compiler_types.h:498:23: note: expanded from macro '_compiletime_assert'
> 498 | __compiletime_assert(condition, msg, prefix, suffix)
> | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ././include/linux/compiler_types.h:490:9: note: expanded from macro '__compiletime_assert'
> 490 | if (!(condition)) \
> | ^~~~~~~~~
> 1 warning generated.
>
>> + writel(val, vec_ctrl);
>> +
>> + /* Read back to flush the update */
>> + val = readl(vec_ctrl);
>> +
>> +err_out:
>> + msi_unlock_descs(&pdev->dev);
>> + return err;
>> +}
>
> ...