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

From: Philippe Reynes
Date: Tue May 12 2015 - 18:21:22 EST

Hi Uwe,

On 12/05/15 09:01, Uwe Kleine-König wrote:

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@xxxxxxxxx>
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@1002b000 {
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.

Ok, I understand, thanks for this explaination.

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.

I've send a new patch (v2 and v3) that map 4 Kbyte for fec registers on imx27.

Best regards

Best regards,

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