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

[Sergei Shtylyov]

Hello.

On 06/30/2014 07:44 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.

   Actually, even to the SATA specs. :-)

> > 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.

   You've looked in a wrong place -- since SControl is a standard *SATA* 
register, it gets read/written by the libata core. The low-level driver only 
provides scr_{read|write}() methods.

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

   It's usually libata's task to negotiate the SATA speed.

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

   Thanks.

> Antoine

WBR, Sergei

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