Re: [PATCH v3 2/2] i2c: cadence: Add support for Axiado AX3000

[Michal Simek <michal.simek@amd.com>]

On 7/1/26 06:48, Swark Yang wrote:
> The Axiado AX3000 SoC integrates a Cadence I2C controller
> that supports SMBus Quick commands.
> 
> Introduce the "axiado,ax3000-i2c" compatible string and
> add a new quirk CDNS_I2C_ENABLE_SMBUS_QUICK to enable
> this functionality. This allows the controller to support
> I2C_FUNC_SMBUS_QUICK, enabling features such as bus scanning
> via quick write commands.
> 
> Additionally, enabling SMBus Quick emulation in the I2C core exposes
> the controller to potential 0-length reads. Because the Cadence IP
> does not natively support 0-length reads (writing 0 to the transfer
> size register leaves the hardware in an unsupported state), this patch
> also populates the adapter quirks with I2C_AQ_NO_ZERO_LEN_READ.

nit: Avoid "this patch". Just use ", populate ..."


> This ensures 0-length reads are safely rejected by the core, preventing
> potential bus hangs.
> 
> Signed-off-by: Swark Yang <syang@axiado.com>
> ---
>   drivers/i2c/busses/i2c-cadence.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index 0fb728ade92e..1964ea1650c5 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -128,6 +128,7 @@
>   #define CDNS_I2C_TIMEOUT_MAX	0xFF
>   
>   #define CDNS_I2C_BROKEN_HOLD_BIT	BIT(0)
> +#define CDNS_I2C_ENABLE_SMBUS_QUICK	BIT(1)
>   #define CDNS_I2C_POLL_US	100000
>   #define CDNS_I2C_POLL_US_ATOMIC	10
>   #define CDNS_I2C_TIMEOUT_US	500000
> @@ -1175,10 +1176,14 @@ static int cdns_i2c_master_xfer_atomic(struct i2c_adapter *adap, struct i2c_msg
>    */
>   static u32 cdns_i2c_func(struct i2c_adapter *adap)
>   {
> +	struct cdns_i2c *id = adap->algo_data;
>   	u32 func = I2C_FUNC_I2C | I2C_FUNC_10BIT_ADDR |
>   			(I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK) |
>   			I2C_FUNC_SMBUS_BLOCK_DATA;
>   
> +	if (id->quirks & CDNS_I2C_ENABLE_SMBUS_QUICK)
> +		func |= I2C_FUNC_SMBUS_QUICK;
> +
>   #if IS_ENABLED(CONFIG_I2C_SLAVE)
>   	func |= I2C_FUNC_SLAVE;
>   #endif
> @@ -1442,9 +1447,24 @@ static const struct cdns_platform_data r1p10_i2c_def = {
>   	.quirks = CDNS_I2C_BROKEN_HOLD_BIT,
>   };
>   
> +static const struct cdns_platform_data ax3000_i2c_def = {
> +	.quirks = CDNS_I2C_ENABLE_SMBUS_QUICK,
> +};
> +
> +/*
> + * The controller does not support zero-length reads. Enabling SMBus Quick
> + * commands would otherwise let the core emulate a Quick read as a zero-length
> + * read message, which writes 0 to the transfer size register and leaves the
> + * hardware in an unsupported state. Reject such transfers in the core.
> + */
> +static const struct i2c_adapter_quirks cdns_i2c_quirks = {
> +	.flags = I2C_AQ_NO_ZERO_LEN_READ,
> +};
> +
>   static const struct of_device_id cdns_i2c_of_match[] = {
>   	{ .compatible = "cdns,i2c-r1p10", .data = &r1p10_i2c_def },
>   	{ .compatible = "cdns,i2c-r1p14",},
> +	{ .compatible = "axiado,ax3000-i2c", .data = &ax3000_i2c_def },
>   	{ /* end of table */ }
>   };
>   MODULE_DEVICE_TABLE(of, cdns_i2c_of_match);
> @@ -1510,6 +1530,9 @@ static int cdns_i2c_probe(struct platform_device *pdev)
>   		id->quirks = data->quirks;
>   	}
>   
> +	if (id->quirks & CDNS_I2C_ENABLE_SMBUS_QUICK)
> +		id->adap.quirks = &cdns_i2c_quirks;
> +
>   	id->rinfo.pinctrl = devm_pinctrl_get(&pdev->dev);
>   	if (IS_ERR(id->rinfo.pinctrl)) {
>   		int err = PTR_ERR(id->rinfo.pinctrl);
> 

Wiring looks good to me.

Acked-by: Michal Simek <michal.simek@amd.com>

Thanks,
Michal