linux-kernel - Re: [PATCH] imx27: dt: only map 1 Kbyte for fec registers

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Message-ID: <20150512070117.GV12671@pengutronix.de>
Date:	Tue, 12 May 2015 09:01:17 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Philippe Reynes <tremyfr@...il.com>
Cc:	Shawn Guo <shawnguo@...nel.org>, mark.rutland@....com,
	devicetree@...r.kernel.org, linux@....linux.org.uk,
	pawel.moll@....com, ijc+devicetree@...lion.org.uk,
	linux-kernel@...r.kernel.org, robh+dt@...nel.org,
	kernel@...gutronix.de, galak@...eaurora.org, shawn.guo@...aro.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] imx27: dt: only map 1 Kbyte for fec registers

Hello,

On Mon, May 11, 2015 at 11:25:08PM +0200, Philippe Reynes wrote:
> On 11/05/15 14:01, Shawn Guo wrote:
> >On Sat, May 09, 2015 at 10:54:30PM +0200, Philippe Reynes wrote:
> >>According to the imx27 documentation, fec has a 1 Kbyte
> >>memory space map, spitted in two regions of 512 bytes.
> >>The first one for control/status registers, and the
> >>second one for event/statistic registers. So, we don't
> >>need to map 16 Kbyte for registers, 1 Kbyte is enough.
> >>
> >>Signed-off-by: Philippe Reynes<tremyfr@...il.com>
> >>---
> >>  arch/arm/boot/dts/imx27.dtsi |    2 +-
> >>  1 files changed, 1 insertions(+), 1 deletions(-)
> >>
> >>diff --git a/arch/arm/boot/dts/imx27.dtsi b/arch/arm/boot/dts/imx27.dtsi
> >>index 6951b66..56bb917 100644
> >>--- a/arch/arm/boot/dts/imx27.dtsi
> >>+++ b/arch/arm/boot/dts/imx27.dtsi
> >>@@ -533,7 +533,7 @@
> >>
> >>  			fec: ethernet@...2b000 {
> >>  				compatible = "fsl,imx27-fec";
> >>-				reg =<0x1002b000 0x4000>;
> >>+				reg =<0x1002b000 0x400>;
> >
> >No.  Per MCIMX27RM.pdf, Table 2-7. AIPI2 Memory Map, it should be 4KiB.
> 
> I agree, this table show that 4KiB is reserved for fec registers.
> But, in paragraph 29.6.1, there is :
> "The FEC implementation requires a 1-Kbyte memory map space"
> So I've thought that 1 Kbye is enough for the register memory space.
The table 2-7 suggests that 4 KiB are routed to the fec even though the
fec module might only make use of the first 1 KiB. That's no
contradiction. The convention used in the device trees is that the first
amount is used.

> I'm pleased to understand that we're both agree that 16 Kbyte is too large.
> 
> If you prefer 4 Kbyte, I'll send a v2 of this patch with this value.
Yes please. In the commit log you might want to point out that a length
of 16 KiB overlaps with the (currently unused?) Security Controller
(SCC) of the i.MX27.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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