linux-kernel - Re: [PATCH v6 4/7] drm/i915: Convert REG_GENMASK*() to fixed-width GENMASK

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Message-ID: <f6885fdb-4361-428c-b6dd-54cd2ac7904d@wanadoo.fr>
Date: Wed, 19 Mar 2025 13:37:32 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: Jani Nikula <jani.nikula@...ux.intel.com>,
 Yury Norov <yury.norov@...il.com>
Cc: Lucas De Marchi <lucas.demarchi@...el.com>,
 Rasmus Villemoes <linux@...musvillemoes.dk>,
 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>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v6 4/7] drm/i915: Convert REG_GENMASK*() to fixed-width
 GENMASK_U*()

On 19/03/2025 at 07:32, Jani Nikula wrote:
> On Tue, 18 Mar 2025, Yury Norov <yury.norov@...il.com> wrote:
>> On Sat, Mar 08, 2025 at 01:48:51AM +0900, Vincent Mailhol via B4 Relay wrote:
>>> From: Lucas De Marchi <lucas.demarchi@...el.com>
>>>
>>> Now that include/linux/bits.h implements fixed-width GENMASK_U*(), use
>>> them to implement the i915/xe specific macros. Converting each driver
>>> to use the generic macros are left for later, when/if other
>>> driver-specific macros are also generalized.
>>>
>>> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
>>> Acked-by: Jani Nikula <jani.nikula@...el.com>
>>> Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
>>> ---
>>> Changelog:
>>>
>>>   v5 -> v6:
>>>
>>>     - No changes.
>>>
>>>   v4 -> v5:
>>>
>>>     - Add braket to macro names in patch description,
>>>       e.g. 'REG_GENMASK*' -> 'REG_GENMASK*()'
>>>
>>>   v3 -> v4:
>>>
>>>     - Remove the prefixes in macro parameters,
>>>       e.g. 'REG_GENMASK(__high, __low)' -> 'REG_GENMASK(high, low)'
>>> ---
>>>  drivers/gpu/drm/i915/i915_reg_defs.h | 108 ++++-------------------------------
>>>  1 file changed, 11 insertions(+), 97 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_reg_defs.h b/drivers/gpu/drm/i915/i915_reg_defs.h
>>> index e251bcc0c89f5710125bc70f07851b2cb978c89c..39e5ed9511174b8757b9201bff735fa362651b34 100644
>>> --- a/drivers/gpu/drm/i915/i915_reg_defs.h
>>> +++ b/drivers/gpu/drm/i915/i915_reg_defs.h
>>> @@ -9,76 +9,19 @@
>>>  #include <linux/bitfield.h>
>>>  #include <linux/bits.h>
>>>  
>>> -/**
>>> - * REG_BIT() - Prepare a u32 bit value
>>> - * @__n: 0-based bit number
>>> - *
>>> - * Local wrapper for BIT() to force u32, with compile time checks.
>>> - *
>>> - * @return: Value with bit @__n set.
>>> +/*
>>> + * Wrappers over the generic BIT_* and GENMASK_* implementations,
>>> + * for compatibility reasons with previous implementation
>>>   */
>>> -#define REG_BIT(__n)							\
>>> -	((u32)(BIT(__n) +						\
>>> -	       BUILD_BUG_ON_ZERO(__is_constexpr(__n) &&		\
>>> -				 ((__n) < 0 || (__n) > 31))))
>>> +#define REG_GENMASK(high, low)		GENMASK_U32(high, low)
>>> +#define REG_GENMASK64(high, low)	GENMASK_U64(high, low)
>>> +#define REG_GENMASK16(high, low)	GENMASK_U16(high, low)
>>> +#define REG_GENMASK8(high, low)		GENMASK_U8(high, low)
>>
>> Nit. Maybe just
>>
>>  #define REG_GENMASK		GENMASK_U32
> 
> Please just keep it as it is for clarity.

I also prefer when the argument is clearly displayed. It shows at first
glance that this is a function-like macro and reminds of the correct
order of the argument without having to look at the definitions in
bits.h. It also allows for people to grep "#define REG_GENMASK(" in
order to find the macro definition.

To be honest, I don't have a strong opinion either, but because Jani
also prefers it this way, I will keep as-is.


Yours sincerely,
Vincent Mailhol