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From:   "Bjoern A. Zeeb" <bz@FreeBSD.org>
To:     "Kalle Valo" <kvalo@codeaurora.org>
Cc:     linux-wireless@vger.kernel.org, luciano.coelho@intel.com
Subject: Re: [PATCH iwlwifi-next] iwlwifi: de-const properly where needed
Date:   Wed, 10 Mar 2021 12:31:05 +0000
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On 1 Mar 2021, at 7:23, Kalle Valo wrote:

> "Bjoern A. Zeeb" <bz@FreeBSD.ORG> writes:
>
>> In order to de-const variables simply casting through (void *) is
>> not enough: "cast from 'const .. *' to 'void *' drops const 
>> qualifier".
>> Cast through (uintptr_t) as well [1] to make this compile on systems
>> with more strict requirements.
>> In addition passing const void *data to dma_map_single() also
>> drops the (const) qualifier.  De-constify on variable on assignment
>> which may be overwritten later.  In either case the (void *) cast
>> to dma_map_single() is not needed (anymore) either.
>>
>> [1] See __DECONST() in sys/sys/cdefs.h in FreeBSD
>>
>> Sponsored-by:  The FreeBSD Foundation
>> Signed-off-by: Bjoern A. Zeeb <bz@FreeBSD.ORG>
>
> Why are we using the const in the first place? That sounds like a bug 
> to
> me.

For the he_cap cases I’ll leave this to Intel to answer as they added 
the
comment that it is writeable.


For the dma_map_single(.., DMA_TO_DEVICE) having const data is probably 
okay.
This seems more (and I can only say from the distance not knowing Linux 
internals)
that the Linux KPI doesn’t/cannot cater for it.  I am not sure why it 
would need
to change a virtual address along the lines and the argument is not 
“const”.


> BTW, your patches are hard to read due to excessive context, I guess 
> you
> are using a very large context value with diff? Our recommendation is 
> to
> use git with default values, see the wiki below for more info.

Sorry.  I’ll fix the three casts you mentioned on the other review and 
send out
v2 with less context for all of them.


Best Regards,
Bjoern