Re: [PATCH v3] usb: typec: fsa4480: Check if the chip is really there

[Heikki Krogerus]

On Mon, Jul 29, 2024 at 10:42:58AM +0200, Konrad Dybcio wrote:
> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
> 
> Currently, the driver will happily register the switch/mux devices, and
> so long as the i2c master doesn't complain, the user would never know
> there's something wrong.
> 
> Add a device id check (based on [1]) and return -ENODEV if the read
> fails or returns nonsense.
> 
> Checking the value on a Qualcomm SM6115P-based Lenovo Tab P11 tablet,
> the ID mentioned in the datasheet does indeed show up:
>  fsa4480 1-0042: Found FSA4480 v1.1 (Vendor ID = 0)
> 
> [1] https://www.onsemi.com/pdf/datasheet/fsa4480-d.pdf
> 
> Fixes: 1dc246320c6b ("usb: typec: mux: Add On Semi fsa4480 driver")
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>

Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>

> ---
> Changes in v3:
> - Don't sign off twice
> - Pick up Dmitry's rb
> - Link to v2: https://lore.kernel.org/r/20240726-topic-fs4480_check-v2-1-901ca449db15@xxxxxxxxxx
> 
> Changes in v2:
> - Prepend the new defines with FSA4480_ to make them more obvious
> - Link to v1: https://lore.kernel.org/r/20240212-topic-fs4480_check-v1-1-d9969e4d6f9a@xxxxxxxxxx
> ---
>  drivers/usb/typec/mux/fsa4480.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/usb/typec/mux/fsa4480.c b/drivers/usb/typec/mux/fsa4480.c
> index cb7cdf90cb0a..cd235339834b 100644
> --- a/drivers/usb/typec/mux/fsa4480.c
> +++ b/drivers/usb/typec/mux/fsa4480.c
> @@ -13,6 +13,10 @@
>  #include <linux/usb/typec_dp.h>
>  #include <linux/usb/typec_mux.h>
>  
> +#define FSA4480_DEVICE_ID	0x00
> + #define FSA4480_DEVICE_ID_VENDOR_ID	GENMASK(7, 6)
> + #define FSA4480_DEVICE_ID_VERSION_ID	GENMASK(5, 3)
> + #define FSA4480_DEVICE_ID_REV_ID	GENMASK(2, 0)
>  #define FSA4480_SWITCH_ENABLE	0x04
>  #define FSA4480_SWITCH_SELECT	0x05
>  #define FSA4480_SWITCH_STATUS1	0x07
> @@ -251,6 +255,7 @@ static int fsa4480_probe(struct i2c_client *client)
>  	struct typec_switch_desc sw_desc = { };
>  	struct typec_mux_desc mux_desc = { };
>  	struct fsa4480 *fsa;
> +	int val = 0;
>  	int ret;
>  
>  	fsa = devm_kzalloc(dev, sizeof(*fsa), GFP_KERNEL);
> @@ -268,6 +273,15 @@ static int fsa4480_probe(struct i2c_client *client)
>  	if (IS_ERR(fsa->regmap))
>  		return dev_err_probe(dev, PTR_ERR(fsa->regmap), "failed to initialize regmap\n");
>  
> +	ret = regmap_read(fsa->regmap, FSA4480_DEVICE_ID, &val);
> +	if (ret || !val)
> +		return dev_err_probe(dev, -ENODEV, "FSA4480 not found\n");
> +
> +	dev_dbg(dev, "Found FSA4480 v%lu.%lu (Vendor ID = %lu)\n",
> +		FIELD_GET(FSA4480_DEVICE_ID_VERSION_ID, val),
> +		FIELD_GET(FSA4480_DEVICE_ID_REV_ID, val),
> +		FIELD_GET(FSA4480_DEVICE_ID_VENDOR_ID, val));
> +
>  	/* Safe mode */
>  	fsa->cur_enable = FSA4480_ENABLE_DEVICE | FSA4480_ENABLE_USB;
>  	fsa->mode = TYPEC_STATE_SAFE;

thanks,

-- 
heikki