linux-kernel - Re: [PATCHv7] EDAC, altera: Add Altera L2 Cache and OCRAM EDAC Support

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Date:	Mon, 4 Jan 2016 15:33:23 -0600
From:	Thor Thayer <tthayer@...nsource.altera.com>
To:	Borislav Petkov <bp@...en8.de>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>
CC:	<dinh.linux@...il.com>, <dougthompson@...ssion.com>,
	<mchehab@....samsung.com>, <linux@....linux.org.uk>,
	<linux-edac@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv7] EDAC, altera: Add Altera L2 Cache and OCRAM EDAC
 Support

On 01/04/2016 03:07 PM, Borislav Petkov wrote:
> On Mon, Jan 04, 2016 at 02:55:43PM -0600, Dinh Nguyen wrote:
>> Right. So for us, if we build in SDRAM ECC unconditionally, there is a
>> requirement with the bootloader to turn on ECC and scrub the memory.
>
> Huh, how does a built-in piece of code cause the bootloader to do
> something?!?
>
> And how would the bootloader know what's in the kernel? The bootloader
> runs first and hands off to the kernel...
>
Hi Boris,

The decision about ECC or non-ECC SDRAM is made before building the 
Linux image and must be matched to the appropriate bootloader (ECC or 
non-ECC).

If ECC is desired for SDRAM, the bootloader enables SDRAM ECC and then 
initializes the memory contents (scrub) before the Linux image is loaded 
into SDRAM.

The ECC syndromes are calculated and stored in SDRAM only when SDRAM ECC 
is enabled and the SDRAM data is written (in the bootloader case, this 
is the Linux image). If we suddenly switched ECC on during Linux 
initialization, we'd be flooded with ECC errors since the ECC syndromes 
won't match the data for the Linux image.

The scrubbing process takes more time to boot which some of our 
customers don't want. This is what Dinh was referring to.
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