RE: [RFC] ioat-dca: force I/OAT DCA when disabled in BIOS

[Sosnowski, Maciej]

Brice Goglin wrote:
>> While this patch should work for some platforms (with I/OAT devices of IDs: 0x1a38, 0x360b,
>> 0x65ff) it is not a platform generic solution. Generally enabling DCA, like this dca_force()
>> routine does, requires other settings including the tag_map which should be set by BIOS. Thus
>> it should be BIOS responsibility to prepare the whole required configuration for DCA. 
> 
> Well, that's exactly the reason why the patch only enforces DCA when
> ioat_dca_force=1 is given. We obviously don't want to tweak registers
> like this by default, unless the admin knows what he is doing.

As we can't guarantee that dca_force() should work on all platforms,
we can't accept adding this functionality as a part of the driver - even if it's disbled by default.
If an admin wishes to take a chance he can use the userspace program.

> Having to run a custom script is really annoying for many Dell machine
> users where the tag_map is already correctly set by the BIOS. And you
> have to make sure that the script runs before ioatdma is loaded (which
> means you cannot built ioatdma inside the kernel, by the way).
> 
> By the way, do you have some ideas about how to filter bridges better?
> Maybe somebody at Intel has a whitelist of intel bridges that could be
> involved here?

What I found is that the list will be all root ports for the 5000-series chipset (Blackford),
5100-series chipset (San Clemente), 7300 chipset (Caneland).
The register does not exist for 5400 chipset (Seaburg).

Regards,
Maciej--
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