linux-kernel - Re: [PATCH] net: ethernet: fs-enet: remove casting dma_alloc

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Message-ID: <4a1c2852-781f-e125-afcb-69387660b6af@csgroup.eu>
Date:   Fri, 11 Dec 2020 17:42:56 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     David Laight <David.Laight@...LAB.COM>,
        Xu Wang <vulab@...as.ac.cn>,
        "pantelis.antoniou@...il.com" <pantelis.antoniou@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: ethernet: fs-enet: remove casting dma_alloc_coherent



Le 11/12/2020 à 17:07, David Laight a écrit :
> From: Christophe Leroy
>> Sent: 11 December 2020 15:22
>>
>> Le 11/12/2020 à 09:52, Xu Wang a écrit :
>>> Remove casting the values returned by dma_alloc_coherent.
>>
>> Can you explain more in the commit log ?
>>
>> As far as I can see, dma_alloc_coherent() doesn't return __iomem, and ring_base member is __iomem
> 
> Which is probably wrong - that is the kernel address of kernel memory.
> So it shouldn't have the __iomem marker.

That's where the buffer descriptors are, the driver accesses to the content of the buffer 
descriptors using the IO accessors in_be16()/out_be16(). Is it not correct ?

Christophe

> 
> I wonder what else is wrong....
> 
> 	David
> 
>>
>> Christophe
>>
>>>
>>> Signed-off-by: Xu Wang <vulab@...as.ac.cn>
>>> ---
>>>    drivers/net/ethernet/freescale/fs_enet/mac-fec.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/ethernet/freescale/fs_enet/mac-fec.c
>> b/drivers/net/ethernet/freescale/fs_enet/mac-fec.c
>>> index 99fe2c210d0f..3ae345676e50 100644
>>> --- a/drivers/net/ethernet/freescale/fs_enet/mac-fec.c
>>> +++ b/drivers/net/ethernet/freescale/fs_enet/mac-fec.c
>>> @@ -131,7 +131,7 @@ static int allocate_bd(struct net_device *dev)
>>>    	struct fs_enet_private *fep = netdev_priv(dev);
>>>    	const struct fs_platform_info *fpi = fep->fpi;
>>>
>>> -	fep->ring_base = (void __force __iomem *)dma_alloc_coherent(fep->dev,
>>> +	fep->ring_base = dma_alloc_coherent(fep->dev,
>>>    					    (fpi->tx_ring + fpi->rx_ring) *
>>>    					    sizeof(cbd_t), &fep->ring_mem_addr,
>>>    					    GFP_KERNEL);
>>>
> 
> -
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