linux-kernel - Re: [RFC PATCH 1/4] EDAC: mvebu: Add driver for Marvell Armada SoCs

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Date:   Thu, 22 Jun 2017 21:43:05 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Jan Lübbe <jlu@...gutronix.de>
CC:     "bp@...en8.de" <bp@...en8.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/4] EDAC: mvebu: Add driver for Marvell Armada SoCs

On 23/06/17 02:37, Jan Lübbe wrote:
> Hi Chris,
> 
> On Fr, 2017-06-09 at 15:14 +0200, Jan Lübbe wrote:
>>> +static void mvebu_init_csrows(struct mem_ctl_info *mci,
>>> +                             struct mvebu_mc_pdata *pdata)
>> [...]
>>> +     devtype = (ctl >> 20) & 0x3;
>>> +     switch (devtype) {
>>> +     case 0x0:
>>> +             dimm->dtype = DEV_X32;
>>> +             break;
>>> +     case 0x2:               /* could be X8 too, but no way to tell
>> */
>>> +             dimm->dtype = DEV_X16;
>>> +             break;
>>> +     case 0x3:
>>> +             dimm->dtype = DEV_X4;
>>> +             break;
>>> +     default:
>>> +             dimm->dtype = DEV_UNKNOWN;
>>> +             break;
>>> +     }
>> This register is documented as reserved? I pulled the X8/X16
>> information from the Address Control Register (CSnStruct bits).
> 
> Do you have more information on how to decode the Bus width?
> 
> It's not clear from the MV78230/78x60 docs:
> - The SDRAM Configuration Register, offset 15 bit is:
>    0 = Half (32 bit data bus)
>    1 = Full (64 bit data bus)

For the integrated version it still is just half and full but half == 16 
and full == 32.

> - The SDRAM Address Control Register, offsets 0-1, 4-5, 8-9 and 12-13
> (for CS 0, 1, 3 and 4):
>    0 = X8
>    1 = X16
>    2 and 3 are not documented

This definition is the same for the integrated version.

> Is this clearer in your documentation, so that we can have the same code
> handle both variants? Otherwise, we'd probably need separate DT
> compatibles.

I think we do need to use the compatible string to decide how to 
interpret full/half.