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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Cai Huoqing <caihuoqing@baidu.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Peter Huewe <peterhuewe@gmx.de>,
	linuxppc-dev@lists.ozlabs.org, linux-integrity@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tpm: ibmvtpm: Make use of dma_alloc_coherent()
Date: Tue, 12 Oct 2021 12:43:25 -0300	[thread overview]
Message-ID: <20211012154325.GI2688930@ziepe.ca> (raw)
In-Reply-To: <31619f2f192a4f1584e458f468422cf6e8f7542f.camel@kernel.org>

On Tue, Oct 12, 2021 at 06:29:58PM +0300, Jarkko Sakkinen wrote:
> 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@baidu.com>
> 
> If this does not do functionally anything useful, there's no
> reason to apply this.

At least in this case it looks like the ibmvtpm is not using the DMA
API properly. There is no sync after each data transfer. Replacing
this wrong usage with the coherent API is reasonable.

Jason

WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: linux-kernel@vger.kernel.org, Cai Huoqing <caihuoqing@baidu.com>,
	Paul Mackerras <paulus@samba.org>,
	Peter Huewe <peterhuewe@gmx.de>,
	linuxppc-dev@lists.ozlabs.org, linux-integrity@vger.kernel.org
Subject: Re: [PATCH] tpm: ibmvtpm: Make use of dma_alloc_coherent()
Date: Tue, 12 Oct 2021 12:43:25 -0300	[thread overview]
Message-ID: <20211012154325.GI2688930@ziepe.ca> (raw)
In-Reply-To: <31619f2f192a4f1584e458f468422cf6e8f7542f.camel@kernel.org>

On Tue, Oct 12, 2021 at 06:29:58PM +0300, Jarkko Sakkinen wrote:
> 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@baidu.com>
> 
> If this does not do functionally anything useful, there's no
> reason to apply this.

At least in this case it looks like the ibmvtpm is not using the DMA
API properly. There is no sync after each data transfer. Replacing
this wrong usage with the coherent API is reasonable.

Jason

  reply	other threads:[~2021-10-12 15:43 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-10 16:01 [PATCH] tpm: ibmvtpm: Make use of dma_alloc_coherent() Cai Huoqing
2021-10-10 16:01 ` Cai Huoqing
2021-10-12 15:29 ` Jarkko Sakkinen
2021-10-12 15:29   ` Jarkko Sakkinen
2021-10-12 15:43   ` Jason Gunthorpe [this message]
2021-10-12 15:43     ` Jason Gunthorpe
2021-10-12 17:40     ` Jarkko Sakkinen
2021-10-12 17:40       ` Jarkko Sakkinen
2021-10-12 21:01       ` David Laight
2021-10-12 21:01         ` David Laight

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