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

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Date:	Mon, 11 May 2015 23:25:08 +0200
From:	Philippe Reynes <tremyfr@...il.com>
To:	Shawn Guo <shawnguo@...nel.org>
CC:	shawn.guo@...aro.org, kernel@...gutronix.de, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] imx27: dt: only map 1 Kbyte for fec registers

Hi Shawn,

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.

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.

> Shawn

Regards,
Philippe
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