linux-kernel - Re: [PATCH RFT v3 4/4] hwmon: (spd5118) Add support for reading SPD data

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Message-ID: <b3109c26-dde1-44cf-b431-80957c97de5f@gmx.de>
Date: Sat, 1 Jun 2024 21:23:24 +0200
From: Armin Wolf <W_Armin@....de>
To: Thomas Weißschuh <linux@...ssschuh.net>,
 Guenter Roeck <linux@...ck-us.net>
Cc: linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, linux-kernel@...r.kernel.org,
 René Rebe <rene@...ctcode.de>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: Re: [PATCH RFT v3 4/4] hwmon: (spd5118) Add support for reading SPD
 data

Am 01.06.24 um 16:08 schrieb Thomas Weißschuh:

> On 2024-06-01 06:48:29+0000, Guenter Roeck wrote:
>
> <snip>
>
>> Makes sense. Another question:
>>
>> This:
>>
>> +        struct nvmem_config nvmem_config = {
>> +               .type = NVMEM_TYPE_EEPROM,
>> +               .name = dev_name(dev),
>> +               .id = NVMEM_DEVID_AUTO,
>>
>> results in:
>>
>> $ ls /sys/bus/nvmem/devices
>> 0-00501  0-00512  0-00523  0-00534  cmos_nvram0
>> ^^^^^^^  ^^^^^^^  ^^^^^^^  ^^^^^^^
>>
>> which really doesn't look good. My current plan is to go with NVMEM_DEVID_NONE,
>> which results in
>>
>> $ ls /sys/bus/nvmem/devices
>> 0-0050	0-0051	0-0052	0-0053	cmos_nvram0
>>
>> We could also used fixed strings, but "spd" results in "spd[1-4]" which
>> I think would be a bit misleading since the DDR3/4 SPD data format is
>> different, and "spd5118" would result in "spd5118[1-4]" which again would
>> look odd. Any suggestions ?
> In order of descending, personal preference:
>
> * spd-ddr5-[0-3] (.id = client->address - 0x50)

Hi,

this will break as soon as more than 8 DDR5 DIMMs are installed.

> * spd-ddr5-[0-3] (NVMEM_DEVID_AUTO)
> * Same with only "ddr5-"
> * spd5118-[0-3]
> * Your proposal from above
> * nvmem[0-3] (default handling)
> * 0-0050-[0-3]
>
> Also can't a user of the eeprom already figure out which kind of module
> it is by looking at the eeprom contents?
> The first few bytes used for that seem to be compatible between at least
> DDR4 and DDR5.
>
> So using plain spd[1-4] could be enough.

This could cause problems when DDR6 arrives.
Personally i would prefer the spd5118-X (NVMEM_DEVID_AUTO) format.

Thanks,
Armin Wolf