linux-kernel - Re: [PATCH v2] drivers: ata: wake port before DMA stop for ALPM

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Date:	Mon, 25 Jan 2016 15:23:03 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Danesh Petigara <dpetigara@...adcom.com>
Cc:	linux-ide@...r.kernel.org, f.fainelli@...il.com,
	computersforpeace@...il.com, gregory.0xf0@...il.com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2] drivers: ata: wake port before DMA stop for ALPM

On Mon, Jan 11, 2016 at 01:22:26PM -0800, Danesh Petigara wrote:
> The AHCI driver code stops and starts port DMA engines at will
> without considering the power state of the particular port. The
> AHCI specification isn't very clear on how to handle this scenario,
> leaving implementation open to interpretation.
> 
> Broadcom's STB SATA host controller is unable to handle port DMA
> controller restarts when the port in question is in low power mode.
> When a port enters partial or slumber mode, its PHY is powered down.
> When a controller restart is requested, the controller's internal
> state machine expects the PHY to be brought back up by software which
> never happens in this case, resulting in failures.
> 
> To avoid this situation, logic is added to manually wake up the port
> just before its DMA engine is stopped, if the port happens to be in
> a low power state. HBA initiated power management ensures that the port
> eventually returns to its configured low power state, when the link is
> idle (as per the conditions listed in the spec). A new host flag is also
> added to ensure this logic is only exercised for hosts with the above
> limitation.
> 
> Signed-off-by: Danesh Petigara <dpetigara@...adcom.com>
> Reviewed-by: Markus Mayer <mmayer@...adcom.com>

Applied to libata/for-4.5-fixes w/ some formatting changes.

Thanks.

-- 
tejun