linux-kernel - Re: [PATCH v4 5/6] i2c: smbus: Support DDR5 SPD EEPROMs

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Date: Mon, 17 Jun 2024 08:49:30 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Paul Menzel <pmenzel@...gen.mpg.de>
Cc: linux-hwmon@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	René Rebe <rene@...ctcode.de>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Armin Wolf <W_Armin@....de>,
	Stephen Horvath <s.horvath@...look.com.au>
Subject: Re: [PATCH v4 5/6] i2c: smbus: Support DDR5 SPD EEPROMs

Hi Paul,

On Mon, Jun 17, 2024 at 04:42:47PM +0200, Paul Menzel wrote:
[ ... ]
> 
> I applied your patch
> 
>     $ git log --oneline --no-decorate -2
>     00058a6 eeprom: Add basic spd5118 support
>     a0e5865 i2cdetect: only use "newer" I2C_FUNC_* flags if they exist
> 
> but reading eeprom fails:
> 
>     $ sudo ./eeprom/decode-dimms

decode-dimms does not need sudo, but that should not make a difference.

>     Cannot read /sys/bus/i2c/drivers/spd5118/0-0050/eeprom at
> ./eeprom/decode-dimms line 2465.
> 
Well, it _is_ a hack ;-), but that specific operation should not fail.

Please try the following:

ls -l /sys/bus/i2c/drivers/spd5118/0-0050/eeprom
cp /sys/bus/i2c/drivers/spd5118/0-0050/eeprom /tmp
od -t x1 /sys/bus/i2c/drivers/spd5118/0-0050/eeprom
sudo i2cdump -y -f 0 0x50

All those should work, and the size of /tmp/eeprom should be
1024 bytes. The output of i2cdump should start with something like

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 51 18 0a 86 32 03 32 00 00 00 00 07 ff 7f 00 00    Q???2?2......?..
                                     ^^

and with

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 51 18 0a 86 32 03 32 00 00 00 00 00 ff 7f 00 00    Q???2?2......?..
                                     ^^

after executing the "sensors" command.

Other than that, I can see that your system is an Intel system,
meaning the i2c controller would be i801, not piix4. I wonder
if that makes a difference. Has anyone else seeing this tested
eeprom access with i801 (or any other controller besides piix4),
by any chance ?

Thanks,
Guenter