linux-kernel - Re: [PATCH v7 1/7] phy: add a driver for the Berlin SATA PHY

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Date:	Mon, 30 Jun 2014 17:44:09 +0200
From:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	tj@...nel.org, kishon@...com, thomas.petazzoni@...e-electrons.com,
	zmxu@...vell.com, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	alexandre.belloni@...e-electrons.com, jszhang@...vell.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 1/7] phy: add a driver for the Berlin SATA PHY

Hi Sebastian,

On Mon, Jun 30, 2014 at 04:40:49PM +0200, Sebastian Hesselbarth wrote:
> On 06/30/2014 11:59 AM, Antoine Ténart wrote:
> >On Wed, Jun 25, 2014 at 11:03:25PM +0400, Sergei Shtylyov wrote:
> >>On 06/23/2014 05:39 PM, Antoine Ténart wrote:
> >>>+	/* set the controller speed */
> >>>+	writel(0x31, ctrl_reg + PORT_SCR_CTL);
> >>
> >>    Value undocumented? Or is this the SATA SControl register by chance?
> >
> >Some magic is still there...
> 
> I guess Sergei was referring to AHCI spec here. PORT_SCR bits are
> documented in AHCI spec as:
> 
> 7:4 = 0x3 Limit speed negotiation to a rate not greater than Gen3
>           communication rate.
> 
> 3:0 = 0x1 Perform interface communication sequence [...]. This is
>           functionally equivalent to a hard reset [...].
> 
> So, the question is: Should we really need to reset controller in the
> PHY driver or is it already done in AHCI common code? At least we
> should change the comment to something like
> /* set Gen3 controller speed and perform hard reset */

I just checked, the AHCI common code has a function to do the reset:
ahci_reset_controller(). As of the max speed negociation rate, I did not
see it in the common AHCI functions.

The eSATA port on the Berlin2Q works without this line, but it may be a
good idea to keep the max speed negociation rate.

Anyway, we can remove the reset part. Nice catch!

Antoine

-- 
Antoine Ténart, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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