linux-kernel - Re: [PATCHv6 1/2] add basic register-field manipulation macros

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Message-ID: <8737m3bsau.fsf@kamboji.qca.qualcomm.com>
Date:	Wed, 17 Aug 2016 13:31:21 +0300
From:	Kalle Valo <kvalo@...eaurora.org>
To:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	gregkh@...uxfoundation.org, davem@...emloft.net
Cc:	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	dinan.gunawardena@...ronome.com,
	Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: Re: [PATCHv6 1/2] add basic register-field manipulation macros

Jakub Kicinski <jakub.kicinski@...ronome.com> writes:

> Common approach to accessing register fields is to define
> structures or sets of macros containing mask and shift pair.
> Operations on the register are then performed as follows:
>
>  field = (reg >> shift) & mask;
>
>  reg &= ~(mask << shift);
>  reg |= (field & mask) << shift;
>
> Defining shift and mask separately is tedious.  Ivo van Doorn
> came up with an idea of computing them at compilation time
> based on a single shifted mask (later refined by Felix) which
> can be used like this:
>
>  #define REG_FIELD 0x000ff000
>
>  field = FIELD_GET(REG_FIELD, reg);
>
>  reg &= ~REG_FIELD;
>  reg |= FIELD_PUT(REG_FIELD, field);
>
> FIELD_{GET,PUT} macros take care of finding out what the
> appropriate shift is based on compilation time ffs operation.
>
> GENMASK can be used to define registers (which is usually
> less error-prone and easier to match with datasheets).
>
> This approach is the most convenient I've seen so to limit code
> multiplication let's move the macros to a global header file.
> Attempts to use static inlines instead of macros failed due
> to false positive triggering of BUILD_BUG_ON()s, especially with
> GCC < 6.0.
>
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Reviewed-by: Dinan Gunawardena <dinan.gunawardena@...ronome.com>

Are people ok with this? I think they are useful and I can take these
through my tree, but I would prefer to get an ack from other maintainers
first. Dave? Andrew?

Full patches here:

https://patchwork.kernel.org/patch/9284153/

https://patchwork.kernel.org/patch/9284155/

-- 
Kalle Valo