linux-kernel - Re: [PATCH] i2c: smbus: support new RAM variant for SPD

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Date:   Tue, 8 Nov 2022 11:48:51 +0100
From:   Jean Delvare <jdelvare@...e.de>
To:     Corentin Labbe <clabbe@...libre.com>
Cc:     wsa@...nel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: smbus: support new RAM variant for SPD

Hi Corentin,

On Mon,  7 Nov 2022 16:06:02 +0000, Corentin Labbe wrote:
> On my x05 laptop I got:
> Memory type 0x12 not supported yet, not instantiating SPD


Oh, that one must be old.

> Adding the 0x12 case lead to a successful instantiated SPD AT24 EEPROM.
> i801_smbus 0000:00:1f.3: SMBus using polling
> i2c i2c-6: 2/2 memory slots populated (from DMI)
> at24 6-0050: 256 byte spd EEPROM, read-only
> i2c i2c-6: Successfully instantiated SPD at 0x50
> at24 6-0051: 256 byte spd EEPROM, read-only
> i2c i2c-6: Successfully instantiated SPD at 0x51
> 
> And then, I decoded it successfully via decode-dimms.
> 
> Signed-off-by: Corentin Labbe <clabbe@...libre.com>
> ---
> The result of decode-dimms could be found at http://kernel.montjoie.ovh/zoo/x05/decode-dimms.txt
> Since RAM is DDR, I wanted to add '/* DDR */' comment, but I didnt find any document with
> proof that this 0x12 is for DDR.

It is. The document you are looking for is:
https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.6.0.pdf

and specifically section 7.18.2 (Memory Device — Type), table 78
(Memory Device: Type).

> 
>  drivers/i2c/i2c-smbus.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
> index 07c92c8495a3..6dca19c994db 100644
> --- a/drivers/i2c/i2c-smbus.c
> +++ b/drivers/i2c/i2c-smbus.c
> @@ -362,6 +362,7 @@ void i2c_register_spd(struct i2c_adapter *adap)
>  	}
>  
>  	switch (common_mem_type) {
> +	case 0x12:
>  	case 0x13:	/* DDR2 */
>  	case 0x18:	/* DDR3 */
>  	case 0x1C:	/* LPDDR2 */

Please also add LPDDR (0x1B) for consistency.

Thanks,
-- 
Jean Delvare
SUSE L3 Support