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Re: [PATCH 09/14] ata: Use 32bit DMA in AHCI for Loongson 3.

To: Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 09/14] ata: Use 32bit DMA in AHCI for Loongson 3.
From: Huacai Chen <chenhuacai@gmail.com>
Date: Mon, 18 Jun 2012 18:41:58 +0800
Cc: Sergei Shtylyov <sshtylyov@mvista.com>, Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org, Fuxin Zhang <zhangfx@lemote.com>, Zhangjin Wu <wuzhangjin@gmail.com>, Huacai Chen <chenhc@lemote.com>, Hongliang Tao <taohl@lemote.com>, Hua Yan <yanh@lemote.com>, linux-ide@vger.kernel.org
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Ohh, this is because Loongson-3 has a hardware bug, when the HT
controller receive a 64-bit DMA address, the high bits is lost. So set
to 32-bit DMA is just a workaround.

I'm sorry that I didn't describe this clearly.

On Mon, Jun 18, 2012 at 6:10 PM, Borislav Petkov <bp@alien8.de> wrote:
> On Mon, Jun 18, 2012 at 05:04:14PM +0800, huacai chen wrote:
>> Do you means it is a better idea to modify "enum board_ids" and add a
>> new board id such as board_ahci_sb700_loongson, and then add a new
>> entry in ahci_port_info[]?
>> If so, I think there is a problem: the pci id of our AHCI controller
>> is 1002:4390, if I add board_ahci_sb700_loongson, then I should also
>> add
>> { PCI_VDEVICE(ATI, 0x4390), board_ahci_sb700_loongson },
>> in ahci_pci_tbl[], but ahci_pci_tbl[] already has a line
>> { PCI_VDEVICE(ATI, 0x4390), board_ahci_sb700 },
>> Then which entry will match the device?
>
> Before you do anything, my question is:
>
> SB700/800 chipsets don't need to set a 32-bit only DMA flag; why do you
> need it when you use the same chipset?
>
> So why do you need to do 32-bit DMA only when the chipset supports
> 64-bit DMA just fine?
>
> Thanks.
>
> --
> Regards/Gruss,
>    Boris.

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