linux-kernel - Re: [PATCH v2 2/3] soundwire: SDCA: add helper macro to access controls

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <f35a0ae7-2779-0c69-9ef3-0d0e298888ac@linux.intel.com>
Date:   Tue, 8 Sep 2020 08:33:11 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     alsa-devel@...a-project.org, tiwai@...e.de, broonie@...nel.org,
        gregkh@...uxfoundation.org,
        Bard liao <yung-chuan.liao@...ux.intel.com>,
        Rander Wang <rander.wang@...ux.intel.com>,
        Guennadi Liakhovetski <guennadi.liakhovetski@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] soundwire: SDCA: add helper macro to access
 controls

Thanks for the review Vinod,

> This is good, thanks for adding it in changelog. Can you also add this
> description to Documentation (that can come as an individual patch),

ok

>> +/*
>> + * v1.2 device - SDCA address mapping
>> + *
>> + * Spec definition
>> + *	Bits		Contents
>> + *	31		0 (required by addressing range)
>> + *	30:26		0b10000 (Control Prefix)
> 
> So this is for 30:26

I don't get the comment, sorry.

> 
>> + *	25		0 (Reserved)
>> + *	24:22		Function Number [2:0]
>> + *	21		Entity[6]
>> + *	20:19		Control Selector[5:4]
>> + *	18		0 (Reserved)
>> + *	17:15		Control Number[5:3]
>> + *	14		Next
>> + *	13		MBQ
>> + *	12:7		Entity[5:0]
>> + *	6:3		Control Selector[3:0]
>> + *	2:0		Control Number[2:0]
>> + */
>> +
>> +#define SDW_SDCA_CTL(fun, ent, ctl, ch)						\
>> +	(BIT(30)							|	\
> 
> Programmatically this is fine, but then since we are defining for the
> description above, IMO it would actually make sense for this to be defined
> as FIELD_PREP:
> 
>          FIELD_PREP(GENMASK(30, 26), 1)
> 
> or better
> 
>          u32_encode_bits(GENMASK(30, 26), 1)
> 
>> +	FIELD_PREP(GENMASK(24, 22), FIELD_GET(GENMASK(2, 0), (fun)))	|	\
> 
> Why not use u32_encode_bits(GENMASK(24, 22), (fun)) instead for this and
> below?

Because your comment for the v1 review was to use FIELD_PREP/FIELD_GET, 
and your other patches for bitfield access only use FIELD_PREP/FIELD_GET.

I really don't care about which macro is used but it wouldn't hurt to 
have some level of consistency between different parts of the code? Why 
not use FIELD_PREP/GET everywhere?

>> +	FIELD_PREP(BIT(21), FIELD_GET(BIT(6), (ent)))			|	\
>> +	FIELD_PREP(GENMASK(20, 19), FIELD_GET(GENMASK(5, 4), (ctl)))	|	\
>> +	FIELD_PREP(GENMASK(17, 15), FIELD_GET(GENMASK(5, 3), (ch)))	|	\
>> +	FIELD_PREP(GENMASK(12, 7), FIELD_GET(GENMASK(5, 0), (ent)))	|	\
>> +	FIELD_PREP(GENMASK(6, 3), FIELD_GET(GENMASK(3, 0), (ctl)))	|	\
>> +	FIELD_PREP(GENMASK(2, 0), FIELD_GET(GENMASK(2, 0), (ch))))
> 
> Also, can we rather have a nice function for this, that would look much
> cleaner

I am not sure what would be cleaner but fine.

> And while at it, consider defining masks for various fields rather than
> using numbers in GENMASK() above, that would look better, be more
> readable and people can reuse it.

Actually on this one I disagree. These fields are not intended to be 
used by anyone, the goal is precisely to hide them behind regmap, and 
the use of raw numbers makes it easier to cross-check the documentation 
and the code. Adding a separate set of definitions would not increase 
readability.