From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Subject: Re: [PATCH 3.11-rc1] crypto: Fix boot failure due to moduledependency.
Date: Sat, 20 Jul 2013 14:56:06 +0900
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Herbert Xu wrote:
> On Fri, Jul 19, 2013 at 06:31:04PM -0700, Tim Chen wrote:
> >
> > However, when I have the library and generic algorithm compiled in,
> > I do not see the PCLMULQDQ version loaded.
> > 
> > CONFIG_CRYPTO_CRCT10DIF=y
> > CONFIG_CRYPTO_CRCT10DIF_PCLMUL=m
> > CONFIG_CRC_T10DIF=y
> 
> That is completely expected.  I don't really think we need to
> do anything about this case.  After all, if the admin wants to
> use the optimised version for CRC_T10DIF then they could simply
> compile that in as well.
> 

Wow! ;-)

But I'd expect something like

 static int __init crc_t10dif_mod_init(void)
 {
+#if !defined(CONFIG_CRC_T10DIF_MODULE) && defined(CONFIG_CRYPTO_CRCT10DIF_PCLMUL_MODULE)
+	printk(KERN_WARNING "Consider CONFIG_CRYPTO_CRCT10DIF_PCLMUL=y for better performance\n");
+#endif
 	crct10dif_tfm = crypto_alloc_shash("crct10dif", 0, 0);
 	return PTR_RET(crct10dif_tfm);
 }

because the admin might not be aware of this implication.