linux-kernel - Re: [PATCH v2] i2c: i801: Do not instantiate spd5118 under SPD Write Disable

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Message-ID: <260d3079-b462-4c22-a66d-93f41d099a45@gmx.de>
Date: Tue, 27 Jan 2026 06:44:13 +0100
From: Armin Wolf <W_Armin@....de>
To: "Yo-Jung (Leo) Lin" <leo.lin@...onical.com>,
 Jean Delvare <jdelvare@...e.com>, Andi Shyti <andi.shyti@...nel.org>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Guenter Roeck <linux@...ck-us.net>,
 "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.com>,
 linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c: i801: Do not instantiate spd5118 under SPD Write
 Disable

Am 13.06.25 um 09:40 schrieb Yo-Jung (Leo) Lin:

> If SPD Write Disable bit in the SMBus is enabled, writing data to
> addresses from 0x50 to 0x57 is forbidden. This may lead to the
> following issues for spd5118 devices:
>
>    1) Writes to the sensor hwmon sysfs attributes will always result
>       in ENXIO.
>
>    2) During system-wide resume, errors may occur during regcache sync,
>       resulting in the following error messages:
>
>       kernel: spd5118 1-0050: failed to write b = 0: -6
>       kernel: spd5118 1-0050: pm: dpm_run_callback(): spd5118_resume [spd5118] returns -6
>       kernel: spd5118 1-0050: pm: failed to resume async: error -6
>
>    3) nvmem won't be usable, because writing to the page selector becomes
>       impossible.
>
> Also, BIOS vendors may choose to set the page to a value != 0 after a board
> reset. This will make the sensor not functional unless its MR11 register
> can be changed, which is impossible due to writes being disabled.
>
> To address these issues, don't instantiate it at all if the SPD Write Disable
> bit is set.

What is the status of this patch? We know of yet another user having problems with
resuming from suspend that could be traced back to the i801 i2c controller having
SPD Write Disable activated.

Are there any problems with this patch that still need to be addressed?

Thanks,
Armin Wolf

> Signed-off-by: Yo-Jung Lin (Leo) <leo.lin@...onical.com>
> ---
> Changes in v2:
> - Fix build failure on some non-x86 archs, by moving __i801_register_spd() out of the CONFIG_X86 && defined CONFIG_DMI region
> - Also fix unused function warning by adding __always_inline.
> - Link to v1: https://lore.kernel.org/r/20250528-for-upstream-not-instantiate-spd5118-v1-1-8216e2d38918@canonical.com
> ---
>   drivers/i2c/busses/i2c-i801.c | 28 +++++++++++++++++++++++-----
>   1 file changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
> index a7f89946dad41..2a56396d88c29 100644
> --- a/drivers/i2c/busses/i2c-i801.c
> +++ b/drivers/i2c/busses/i2c-i801.c
> @@ -978,6 +978,14 @@ static void i801_disable_host_notify(struct i801_priv *priv)
>   	iowrite8(priv->original_slvcmd, SMBSLVCMD(priv));
>   }
>   
> +static inline __maybe_unused void __i801_register_spd(struct i801_priv *priv)
> +{
> +	if (priv->original_hstcfg & SMBHSTCFG_SPD_WD)
> +		i2c_register_spd_write_disable(&priv->adapter);
> +	else
> +		i2c_register_spd_write_enable(&priv->adapter);
> +}
> +
>   static const struct i2c_algorithm smbus_algorithm = {
>   	.smbus_xfer	= i801_access,
>   	.functionality	= i801_func,
> @@ -1157,6 +1165,19 @@ static void dmi_check_onboard_devices(const struct dmi_header *dm, void *adap)
>   	}
>   }
>   
> +#ifdef CONFIG_I2C_I801_MUX
> +static void i801_register_spd(struct i801_priv *priv)
> +{
> +	if (!priv->mux_pdev)
> +		__i801_register_spd(priv);
> +}
> +#else
> +static void i801_register_spd(struct i801_priv *priv)
> +{
> +	__i801_register_spd(priv);
> +}
> +#endif
> +
>   /* Register optional targets */
>   static void i801_probe_optional_targets(struct i801_priv *priv)
>   {
> @@ -1177,10 +1198,7 @@ static void i801_probe_optional_targets(struct i801_priv *priv)
>   		dmi_walk(dmi_check_onboard_devices, &priv->adapter);
>   
>   	/* Instantiate SPD EEPROMs unless the SMBus is multiplexed */
> -#ifdef CONFIG_I2C_I801_MUX
> -	if (!priv->mux_pdev)
> -#endif
> -		i2c_register_spd_write_enable(&priv->adapter);
> +	i801_register_spd(priv);
>   }
>   #else
>   static void __init input_apanel_init(void) {}
> @@ -1283,7 +1301,7 @@ static int i801_notifier_call(struct notifier_block *nb, unsigned long action,
>   		return NOTIFY_DONE;
>   
>   	/* Call i2c_register_spd for muxed child segments */
> -	i2c_register_spd_write_enable(to_i2c_adapter(dev));
> +	__i801_register_spd(priv);
>   
>   	return NOTIFY_OK;
>   }
>
> ---
> base-commit: 0bb71d301869446810a0b13d3da290bd455d7c78
> change-id: 20250526-for-upstream-not-instantiate-spd5118-463225b346a0
>
> Best regards,