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SubjectRe: [PATCH] add boot option to control Intel combined mode behavior (to allow DMA in combined mode configs!)
Jesse Barnes wrote:
> Combined mode sucks. Especially when both libata and the legacy IDE
> drivers try to drive ports on the same device, since that makes DMA
> rather difficult.
>
> This patch addresses the problem by allowing the user to control which
> driver binds to the ports in a combined mode configuration. In many
> cases, they'll probably want the libata driver to control both ports
> since it can use DMA for talking with ATAPI devices (when
> libata.atapi_enabled=1 of course). It also allows the user to get old
> school behavior by letting the legacy IDE driver bind to both ports.
> But neither is forced, the patch doesn't change current behavior unless
> one of intel_combined_mode=ide or intel_combined_mode=libata is passed
> on the boot line. Either of those options may require you to access
> your devices via different device nodes (/dev/hd* in the ide case
> and /dev/sd* in the libata case), though of course if you have udev
> installed nicely you may not notice anything. :)
>
> Let me know if the documentation is too cryptic, I'd be happy to expand
> on it if necessary. I think most users will want to boot with
> 'intel_combined_mode=libata' and add 'options libata atapi_enabled=1'
> to their modules.conf to get good DVD playing and disk behavior
> (haven't tested CD or DVD writing though).
>
> Documentation/kernel-parameters.txt | 7 +++++++
> drivers/pci/quirks.c | 30 ++++++++++++++++++++++++++++
>
> I'd much rather things behave sanely by default (i.e. DMA for devices on
> both ports), but apparently that's difficult given the various chip
> bugs and hardware configs out there (not to mention that people's
> drives may suddenly change from /dev/hdc to /dev/sdb), so this boot
> option may be the correct long term fix.
>
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Seems like it should work. I presume you tested this?

Remove the 'intel_' prefix from the kernel parameter, since this concept
applies to other controllers as well. Otherwise, seems OK.

Jeff



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