linux-kernel - Re: Driver: PCIe: 'pci_map_sg' returning invalid bus address?

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Message-ID: <4C594D78.6090407@cyconix.com>
Date:	Wed, 04 Aug 2010 12:22:32 +0100
From:	Evan Lavelle <sa212+lkml@...onix.com>
To:	linux-kernel@...r.kernel.org
CC:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: Driver: PCIe: 'pci_map_sg' returning invalid bus address?

FUJITA Tomonori wrote:
>> Made some progress here. The problem is that this is 32-bit PAE kernel, 
>> so 'dma_addr_t' is 64-bit. However, I have a 32-bit PCIe card, so I need 
>> a 32-bit dma_addr_t. How do I do this? In other words, how do I handle 
>> 32-bit PCI cards on PAE or 64-bit systems? My code sets the DMA mask to 
>> 32 bits but this is *not* sufficient:
>>
>> pci_set_dma_mask(my_dev, DMA_32BIT_MASK)
> 
> It doesn't work on x86_32 kernel if your driver doesn't work with the
> block layer or the network subsystem.

Sorry, not sure that I understand this. Are you saying that I can't set 
a DMA mask on x86_32 unless I have a block or network driver?

> If your driver can't handle 64bit DMA, you need bounce buffer. 

The problem is not that I can't handle 64-bit DMA in the driver, but 
that the PCI card can't do 64-bit DMA. I tell the kernel this by calling 
'pci_set_dma_mask' with a 32-bit mask, but it appears to be ignoring my 
request and then giving me a 64-bit dma_addr_t for the 32-bit PCI card.

Thanks -

Evan
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