Re: [PATCH #upstream] ahci: start engine only during soft/hard resets

[Jeff Garzik <jgarzik@pobox.com>]

On 07/22/2011 05:41 AM, Tejun Heo wrote:
> This is another attempt at fixing the same problem that 270dac35c2
> (libata: ahci_start_engine compliant to AHCI spec) tried to solve.
> Unfortunately, 270dac35c2 created regressions for a lot more common
> controllers and got reverted.
>
> This specific AHCI IP block becomes a brick if the DMA engine is
> started while DRQ is set.  It is not possible to avoid the condition
> completely but the most common occurrence is caused by spurious use of
> ahci_start_engine() from ahci_start_port() during init sequence.
>
> DMA engine is started after both soft and hard resets and
> ahci_start_port() is always followed by resets, so there is no reason
> to start DMA engine from ahci_start_port().
>
> This patch removes ahci_start_engine() invocation from
> ahci_start_port().  This change makes failure path of
> ahci_port_suspend() leave engine stopped without following resets.
> This is resolved by replacing ahci_start_port() call with
> ata_port_freeze() which forces resets afterwards, which is the better
> behavior anyway.
>
> Signed-off-by: Tejun Heo<tj@kernel.org>
> Reported-by: Brian Norris<computersforpeace@gmail.com>
> Reported-by: Jian Peng<jipeng2005@gmail.com>
> ---
> Jeff, this needs to be tested for a while in linux-next before sending
> it mainline.  Please apply it for 3.1 merge window and let's see
> whether anything explodes.

Stuffed this into branch #upstream-next, which appears periodically for 
situations like this.  #upstream-next will become #upstream after the 
merge window closes.