[PATCH RFC v2 2/4] phy: Add MIPI C-PHY configuration helpers

[Bryan O'Donoghue]

On 16/10/2026 11:57, George Neacsu via B4 Relay wrote:
> From: George Neacsu <geocausa at gmail.com>
> 
> A CSI-2 receiver knows the link frequency of its transmitter, and by the
> V4L2 convention a C-PHY link frequency is half the symbol rate on each
> trio. Add helpers so that the receiver and the PHY do not each open-code
> that conversion, as phy_mipi_dphy_get_default_config_for_hsclk() does
> for D-PHY:
> 
> - phy_mipi_cphy_get_default_config_for_link_freq() fills a
>    configuration from a link frequency and a trio count;
> - phy_mipi_cphy_config_validate() checks for a symbol rate and one to
>    three trios;
> - phy_mipi_cphy_link_freq() gives the link frequency of a configuration.
> 
> They are small enough to be inline, so no new Kconfig symbol is needed.
> 
> Suggested-by: Bryan O'Donoghue <bod at kernel.org>
> Suggested-by: Loic Poulain <loic.poulain at oss.qualcomm.com>
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: George Neacsu <geocausa at gmail.com>
> ---
>   include/linux/phy/phy-mipi-cphy.h | 61 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 61 insertions(+)
> 
> diff --git a/include/linux/phy/phy-mipi-cphy.h b/include/linux/phy/phy-mipi-cphy.h
> index ef6af61de..f6746dcb0 100644
> --- a/include/linux/phy/phy-mipi-cphy.h
> +++ b/include/linux/phy/phy-mipi-cphy.h
> @@ -2,6 +2,10 @@
>   #ifndef __PHY_MIPI_CPHY_H_
>   #define __PHY_MIPI_CPHY_H_
> 
> +#include <linux/errno.h>
> +
> +#define PHY_MIPI_CPHY_MAX_TRIOS		3
> +
>   /**
>    * struct phy_configure_opts_mipi_cphy - MIPI C-PHY configuration set
>    *
> @@ -24,4 +28,61 @@ struct phy_configure_opts_mipi_cphy {
>   	unsigned char		trios;
>   };
> 
> +/**
> + * phy_mipi_cphy_config_validate() - Validate a MIPI C-PHY configuration
> + * @cfg: configuration to check
> + *
> + * Return: 0 if @cfg has a symbol rate and one to three trios, -EINVAL
> + * otherwise.
> + */
> +static inline int
> +phy_mipi_cphy_config_validate(const struct phy_configure_opts_mipi_cphy *cfg)
> +{
> +	if (!cfg->symbol_rate)
> +		return -EINVAL;
> +
> +	if (cfg->trios < 1 || cfg->trios > PHY_MIPI_CPHY_MAX_TRIOS)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +/**
> + * phy_mipi_cphy_get_default_config_for_link_freq() - C-PHY configuration
> + * from a link frequency
> + * @link_freq: link frequency in Hz
> + * @trios: number of active trios
> + * @cfg: configuration to fill
> + *
> + * A C-PHY link frequency is half the symbol rate on each trio, the
> + * convention V4L2 uses for the link frequency of a C-PHY transmitter.
> + *
> + * Return: 0 on success, -EINVAL if the resulting configuration is invalid.
> + */
> +static inline int
> +phy_mipi_cphy_get_default_config_for_link_freq(unsigned long long link_freq,
> +					       unsigned int trios,
> +					       struct phy_configure_opts_mipi_cphy *cfg)
> +{
> +	if (trios > PHY_MIPI_CPHY_MAX_TRIOS)
> +		return -EINVAL;
> +
> +	cfg->symbol_rate = link_freq * 2;
> +	cfg->trios = trios;
> +
> +	return phy_mipi_cphy_config_validate(cfg);
> +}
> +
> +/**
> + * phy_mipi_cphy_link_freq() - Link frequency of a MIPI C-PHY configuration
> + * @cfg: configuration
> + *
> + * Return: the link frequency in Hz, half the symbol rate on each trio.
> + */
> +static inline unsigned long long
> +phy_mipi_cphy_link_freq(const struct phy_configure_opts_mipi_cphy *cfg)
> +{
> +	return cfg->symbol_rate / 2;
> +}
> +
>   #endif /* __PHY_MIPI_CPHY_H_ */
> 
> --
> 2.53.0
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue at linaro.org>