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

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Message-ID: <568B0370.7080500@opensource.altera.com>
Date:	Mon, 4 Jan 2016 17:42:40 -0600
From:	Thor Thayer <tthayer@...nsource.altera.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	<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 04:01 PM, Borislav Petkov wrote:
> On Mon, Jan 04, 2016 at 03:33:23PM -0600, Thor Thayer wrote:
>> 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.
>
> So that still doesn't have any effect on what's compiled in the EDAC
> module, AFAICT. You simply build everything in and depending on
> whether ECC is enabled or not in the bootloader, altera_edac behaves
> accordingly. On a system with ECC *not* enabled, it would simply have
> the SDRAM ECC functionality inactive.
>
> This is no different than an x86 system where you enter the BIOS and
> enable or disable ECC. The EDAC module queries whether ECC has been
> enabled or not and behaves accordingly.
>
OK. I see your point for SDRAM.

However, in the case of OCRAM and L2 cache ECC, we want to be able to 
enable them individually which is what the following does.

 >> -obj-$(CONFIG_EDAC_ALTERA_MC)		+= altera_edac.o
 >> +altr_edac-y				:= altera_edac.o
 >> +obj-$(CONFIG_EDAC_ALTERA_MC)		+= altr_edac.o
 >> +obj-$(CONFIG_EDAC_ALTERA_L2C)		+= altr_edac.o
 >> +obj-$(CONFIG_EDAC_ALTERA_OCRAM)		+= altr_edac.o
 >
 > What are those supposed to accomplish?
 >

and then the defines are also used to conditionally include the L2 or 
OCRAM ECC functions because everything is in one file.

However, the highbank and octeon edacs are split into separate files for 
L2 which Dinh pointed may be cleaner for individual control.

Thanks,

Thor
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