linux-kernel - Re: [PATCH 2/4] phy: rockchip-emmc: configure frequency range and drive impedance

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Message-ID: <20160513210440.GA99074@google.com>
Date:	Fri, 13 May 2016 14:04:40 -0700
From:	Brian Norris <briannorris@...omium.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Shawn Lin <shawn.lin@...k-chips.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Heiko Stuebner <heiko@...ech.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Brian Norris <computersforpeace@...il.com>
Subject: Re: [PATCH 2/4] phy: rockchip-emmc: configure frequency range and
 drive impedance

On Fri, May 13, 2016 at 11:46:33AM -0700, Doug Anderson wrote:
> On Thu, May 12, 2016 at 6:02 PM, Shawn Lin <shawn.lin@...k-chips.com> wrote:
> > On 2016/5/13 6:43, Brian Norris wrote:
> >> @@ -154,6 +167,20 @@ static int rockchip_emmc_phy_power_on(struct phy
> >> *phy)
> >>         struct rockchip_emmc_phy *rk_phy = phy_get_drvdata(phy);
> >>         int ret = 0;
> >>
> >> +       /* DLL operation: 170 to 200 MHz */
> >
> >
> > What is 170 here? Should we expose them to dt instead of hardcoding
> > them?
> 
> This was probably my fault.  I did some searching and found
> <https://arasan.com/wp-content/media/eMMC-5-1-Total-Solution_Rev-1-3.pdf>.
> It appears to be docs for a similar (but not identical) PHY.  We were
> looking at it to try to get more clarity on some bits that were hard
> to understand in the docs we had.
> 
> In that doc there appear to be 3 bits for selecting the DLL operation
> and they have ranges defined.  In Rockchip's PHY there are only 2
> bits.  Thus things don't map totally properly.
> 
> Anyway, comment should probably be removed.

[...]

> So overall:
> 
> * Should re-spin and remove the comment about 170 MHz.
> 
> * I think this could land as-is other than the comment.

Right, will fix the first bullet point.

Brian