linux-kernel - Re: [PATCH v7 1/5] bits: introduce fixed-type GENMASK

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Message-ID: <202c97b2-e99e-4b88-9ac5-171db244b7d0@wanadoo.fr>
Date: Mon, 24 Mar 2025 16:44:29 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Yury Norov <yury.norov@...il.com>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Rasmus Villemoes <linux@...musvillemoes.dk>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Andrew Morton <akpm@...ux-foundation.org>,
 linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, Andi Shyti <andi.shyti@...ux.intel.com>,
 David Laight <David.Laight@...lab.com>, Jani Nikula <jani.nikula@...el.com>
Subject: Re: [PATCH v7 1/5] bits: introduce fixed-type GENMASK_U*()

On 24/03/2025 at 16:22, Andy Shevchenko wrote:
> On Sat, Mar 22, 2025 at 06:23:12PM +0900, Vincent Mailhol via B4 Relay wrote:
>>
>> Add GENMASK_TYPE() which generalizes __GENMASK() to support different
>> types, and implement fixed-types versions of GENMASK() based on it.
>> The fixed-type version allows more strict checks to the min/max values
>> accepted, which is useful for defining registers like implemented by
>> i915 and xe drivers with their REG_GENMASK*() macros.
>>
>> The strict checks rely on shift-count-overflow compiler check to fail
>> the build if a number outside of the range allowed is passed.
>> Example:
>>
>>   #define FOO_MASK GENMASK_U32(33, 4)
>>
>> will generate a warning like:
>>
>>   include/linux/bits.h:51:27: error: right shift count >= width of type [-Werror=shift-count-overflow]
>>      51 |               type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h)))))
>>         |                           ^~
>>
>> While GENMASK_TYPE() is crafted to cover all variants, including the
>> already existing GENMASK(), GENMASK_ULL() and GENMASK_U128(), for the
>> moment, only use it for the newly introduced GENMASK_U*(). The
>> consolidation will be done in a separate change.
> 
> ...
> 
>>  #if !defined(__ASSEMBLY__)
>> +
> 
>> -#else
> 
>> +#else /* defined(__ASSEMBLY__) */
> 
>> -#endif
>> +
>> +#endif /* !defined(__ASSEMBLY__) */
> 
> Up to you, but if new version is needed or maintainer require, I would move the
> above changes either to a separate patch (prerequisite) or dropped them at all.
> These are not big but unneeded churn,

I do not want to drop this. After all the changes, there is a lot of
scrolling between the #if, #else and #endif, and the comments helps to
keep track of which context we are in.

As for putting this into another patch, OK but only if there is a need
for new version for other reasons.


Yours sincerely,
Vincent Mailhol