linux-kernel - Re: [PATCH] tpm: ibmvtpm: Make use of dma_alloc

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Message-ID: <31619f2f192a4f1584e458f468422cf6e8f7542f.camel@kernel.org>
Date:   Tue, 12 Oct 2021 18:29:58 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Cai Huoqing <caihuoqing@...du.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, linuxppc-dev@...ts.ozlabs.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: ibmvtpm: Make use of dma_alloc_coherent()

On Mon, 2021-10-11 at 00:01 +0800, Cai Huoqing wrote:
> Replacing kmalloc/kfree/get_zeroed_page/free_page/dma_map_single/
  ~~~~~~~~~
  Replace

> dma_unmap_single() with dma_alloc_coherent/dma_free_coherent()
> helps to reduce code size, and simplify the code, and coherent
> DMA will not clear the cache every time.
> 
> Signed-off-by: Cai Huoqing <caihuoqing@...du.com>

If this does not do functionally anything useful, there's no
reason to apply this.

It is also missing information why the substitution is possible.

Field tested code is better than clean code, i.e. we don not
risk at having possible new regressions just for a bit nicer
layout...

/Jarkko