linux-kernel - Re: kexec reboot broken with ioatdma?

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Date:	Wed, 16 Dec 2009 16:11:44 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Roland Dreier <rdreier@...co.com>
CC:	Simon Horman <horms@...ge.net.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>
Subject: Re: kexec reboot broken with ioatdma?

Roland Dreier wrote:
>  > from a kexec point of view I believe that the preferred option is the
>  > former - shutdown the device so it can be initialised using standard paths
>  > in the second kernel.
> 
> OK... however I'm not suggesting a separate kexec initialization path,
> simply adding a reset of the device in the standard initialization.
> This would be fairly normal for other types of device; for example, the
> BIOS may have left a NIC in an undefined state due to network boot.  Of
> course BIOS is unlikely to use an IOAT DMA engine but the principle of
> limiting assumptions about platform state still stands I think.

I agree that is more robust if the init path copes with hardware 
arriving in an unknown state.  I'll look into adding a channel reset in 
the init path (something that should probably have been there since the 
beginning).

> From a quick look, it seems tricky to get a clean shutdown of IOAT stuff
> since there doesn't seem to be a clean ordering that makes sure the
> ioatdma stuff is shutdown after everything using it.

The engines may be in use by multiple subsytems (net, raid) so 
coordinating shutdown ordering would indeed be a pain.

--
Dan

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