linux-kernel - Re: [PATCH] soc: fsl: Remove bogus packed attributes from qman.h

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Date:   Tue, 1 Sep 2020 11:56:30 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Leo Li <leoyang.li@....com>
Cc:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] soc: fsl: Remove bogus packed attributes from qman.h

On Tue, Sep 01, 2020 at 01:50:38AM +0000, Leo Li wrote:
>
> Sorry for the late response.  I missed this email previously.
> 
> These structures are descriptors used by hardware, we cannot have _ANY_ padding from the compiler.  The compiled result might be the same with or without the __packed attribute for now, but I think keep it there probably is safer for dealing with unexpected alignment requirements from the compiler in the future.
> 
> Having conflicting alignment requirements warning might means something is wrong with the structure in certain scenario.  I just tried a ARM64 build but didn't see the warnings.  Could you share the warning you got and the build setup?  Thanks.

Just do a COMPILE_TEST build on x86-64:

In file included from ../drivers/crypto/caam/qi.c:12:
../include/soc/fsl/qman.h:259:1: warning: alignment 1 of ‘struct qm_dqrr_entry’ is less than 8 [-Wpacked-not-aligned]
 } __packed;
 ^
../include/soc/fsl/qman.h:292:2: warning: alignment 1 of ‘struct <anonymous>’ is less than 8 [-Wpacked-not-aligned]
  } __packed ern;
  ^

In any case, those packed markers are completely unnecessary because
those structs contain no holes.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt