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

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Message-ID: <6efc219d-29e1-4169-8393-c7e4610347cc@amd.com>
Date: Tue, 17 Sep 2024 09:31:00 -0500
From: Wei Huang <wei.huang2@....com>
To: Simon Horman <horms@...nel.org>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, netdev@...r.kernel.org,
 Jonathan.Cameron@...wei.com, helgaas@...nel.org, corbet@....net,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, alex.williamson@...hat.com, gospo@...adcom.com,
 michael.chan@...adcom.com, ajit.khaparde@...adcom.com,
 somnath.kotur@...adcom.com, andrew.gospodarek@...adcom.com,
 manoj.panicker2@....com, Eric.VanTassell@....com, vadim.fedorenko@...ux.dev,
 bagasdotme@...il.com, bhelgaas@...gle.com, lukas@...ner.de,
 paul.e.luse@...el.com, jing2.liu@...el.com
Subject: Re: [PATCH V5 2/5] PCI/TPH: Add Steering Tag support



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;
>> +}
> 
> ...