Re: [PATCH v3 2/2] platform: chrome: lightbar: Add support for large sequence

[Tzung-Bi Shih <tzungbi@kernel.org>]

On Tue, Jan 27, 2026 at 07:02:59PM -0800, Gwendal Grignou wrote:
> @@ -475,14 +483,22 @@ static ssize_t program_store(struct device *dev, struct device_attribute *attr,
>  	 * and send a program that is too big for the protocol. In order
>  	 * to ensure the latter, we also need to ensure we have extra bytes
>  	 * to represent the rest of the packet.
> +	 * With V3, larger program can be sent, limited only by the EC.
> +	 * Only the protocol limit the payload size.
>  	 */
> -	extra_bytes = sizeof(*param) - sizeof(param->set_program.data);
> -	max_size = min(EC_LB_PROG_LEN, ec->ec_dev->max_request - extra_bytes);
> -	if (count > max_size) {
> -		dev_err(dev, "Program is %u bytes, too long to send (max: %u)",
> -			(unsigned int)count, max_size);
> -
> -		return -EINVAL;
> +	if (lb_version < 3) {
> +		extra_bytes = sizeof(*param) - sizeof(param->set_program.data);
> +		max_size = min(EC_LB_PROG_LEN, ec->ec_dev->max_request - extra_bytes);
> +		if (count > max_size) {
> +			dev_err(dev, "Program is %zu bytes, too long to send (max: %zu)",
> +				count, max_size);
> +
> +			return -EINVAL;
> +		}
> +	} else {
> +		extra_bytes = sizeof(*param) - sizeof(param->set_program) +
> +			sizeof(param->set_program_ex);
> +		max_size = ec->ec_dev->max_request - extra_bytes;

Not sure if you read comments from v1 [1].  I still think the calculation of
`extra_bytes` is tricky.

[1] https://lore.kernel.org/chrome-platform/aXhWlV6SyaAAum-Q@google.com/

> diff --git a/include/linux/platform_data/cros_ec_commands.h b/include/linux/platform_data/cros_ec_commands.h
> index 9cbf024f56c3..144243143034 100644
> --- a/include/linux/platform_data/cros_ec_commands.h
> +++ b/include/linux/platform_data/cros_ec_commands.h
> @@ -2020,6 +2020,17 @@ struct lightbar_program {
>  	uint8_t data[EC_LB_PROG_LEN];
>  } __ec_todo_unpacked;
>  
> +/*
> + * Lightbar program for large sequences. Sequences are sent in pieces, with
> + * increasing offset. The sequences are still limited by the amount reserved in
> + * EC RAM.
> + */
> +struct lightbar_program_ex {
> +	uint16_t offset;
> +	uint8_t size;
> +	uint8_t data[0];
> +} __ec_todo_unpacked;

Not sure if you read comments from v1 [1].  Please use flexible array member
(i.e., []) and evaluate if it needs any flexible array helpers.