Re: [RFC PATCH 03/10] drm/mipi-dsi: add API for manual control over the DSI link power state

[Neil Armstrong <neil.armstrong@linaro.org>]

On 16/10/2023 18:53, Dmitry Baryshkov wrote:
> The MIPI DSI links do not fully fall into the DRM callbacks model. The
> drm_bridge_funcs abstraction. Instead of having just two states (off and
> on) the DSI hosts have separate LP-11 state. In this state the host is
> on, but the video stream is not yet enabled.
> 
> Introduce API that allows DSI bridges / panels to control the DSI host
> power up state.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> ---
>   drivers/gpu/drm/drm_mipi_dsi.c | 31 +++++++++++++++++++++++++++++++
>   include/drm/drm_mipi_dsi.h     | 29 +++++++++++++++++++++++++----
>   2 files changed, 56 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 14201f73aab1..c467162cb7d8 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -428,6 +428,37 @@ int devm_mipi_dsi_attach(struct device *dev,
>   }
>   EXPORT_SYMBOL_GPL(devm_mipi_dsi_attach);
>   
> +bool mipi_dsi_host_power_control_available(struct mipi_dsi_host *host)
> +{
> +	const struct mipi_dsi_host_ops *ops = host->ops;
> +
> +	return ops && ops->power_up;
> +}
> +EXPORT_SYMBOL_GPL(mipi_dsi_host_power_control_available);
> +
> +int mipi_dsi_host_power_up(struct mipi_dsi_host *host)
> +{
> +	const struct mipi_dsi_host_ops *ops = host->ops;
> +
> +	if (!mipi_dsi_host_power_control_available(host))
> +		return -EOPNOTSUPP;
> +
> +	return ops->power_up ? ops->power_up(host) : 0;
> +}
> +EXPORT_SYMBOL_GPL(mipi_dsi_host_power_up);
> +
> +void mipi_dsi_host_power_down(struct mipi_dsi_host *host)
> +{
> +	const struct mipi_dsi_host_ops *ops = host->ops;
> +
> +	if (!mipi_dsi_host_power_control_available(host))
> +		return;
> +
> +	if (ops->power_down)
> +		ops->power_down(host);
> +}
> +EXPORT_SYMBOL_GPL(mipi_dsi_host_power_down);
> +
>   static ssize_t mipi_dsi_device_transfer(struct mipi_dsi_device *dsi,
>   					struct mipi_dsi_msg *msg)
>   {
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index 167742e579e3..e503c3e4d057 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -68,6 +68,8 @@ int mipi_dsi_create_packet(struct mipi_dsi_packet *packet,
>    * @attach: attach DSI device to DSI host
>    * @detach: detach DSI device from DSI host
>    * @transfer: transmit a DSI packet
> + * @power_up: enable DSI link and bring it to the LP-11 state
> + * @power_down: fully disable DSI link
>    *
>    * DSI packets transmitted by .transfer() are passed in as mipi_dsi_msg
>    * structures. This structure contains information about the type of packet
> @@ -81,10 +83,18 @@ int mipi_dsi_create_packet(struct mipi_dsi_packet *packet,
>    * function will seldomly return anything other than the number of bytes
>    * contained in the transmit buffer on success.
>    *
> - * Also note that those callbacks can be called no matter the state the
> - * host is in. Drivers that need the underlying device to be powered to
> - * perform these operations will first need to make sure it's been
> - * properly enabled.
> + * Note: currently there are two modes of DSI power control. Legacy drivers
> + * will call those callbacks no matter the state the host is in. DSI host
> + * drivers that need the underlying device to be powered to perform these
> + * operations will first need to make sure it's been properly enabled.
> + *
> + * Newer drivers will set the @MIPI_DSI_MANUAL_POWERUP flag to indicate that
> + * they will call @mipi_dsi_power_up() and @mipi_dsi_power_down() to control
> + * the link state of the DSI host or they will set @MIPI_DSI_AUTO_POWERUP to
> + * indicate that the driver is fine with the link being powered up in DSI
> + * host's (atomic_)pre_enable() callback and then being disabled in the
> + * (atomic_)post_disable() callback. The transfer callback must only be called
> + * if the DSI host has been powered up and was not brought down.
>    *
>    * Note: some hosts (sunxi) can not send LP commands between HS video
>    * packets. Thus all DSI transfers sent in LP mode should be limited to the
> @@ -97,6 +107,8 @@ struct mipi_dsi_host_ops {
>   		      struct mipi_dsi_device *dsi);
>   	ssize_t (*transfer)(struct mipi_dsi_host *host,
>   			    const struct mipi_dsi_msg *msg);
> +	int (*power_up)(struct mipi_dsi_host *host);
> +	void (*power_down)(struct mipi_dsi_host *host);
>   };
>   
>   /**
> @@ -143,6 +155,10 @@ struct mipi_dsi_host *of_find_mipi_dsi_host_by_node(struct device_node *node);
>   #define MIPI_DSI_MODE_LPM		BIT(11)
>   /* transmit data ending at the same time for all lanes within one hsync */
>   #define MIPI_DSI_HS_PKT_END_ALIGNED	BIT(12)
> +/* DSI peripheral driver manually controls DSI link powerup */
> +#define MIPI_DSI_MANUAL_POWERUP		BIT(13)
> +/* DSI peripheral driver is fine with automatic DSI link power control */
> +#define MIPI_DSI_AUTO_POWERUP		BIT(14)

What happens if none of the bits are in the flags ?

Can't we implement "opportunistic power-up" on the first DSI command sent?

If a bridge/panel sends a DSI command, and if it happens before the DSI host enable, then
the DSI host will "pre-enable" the host and put the link in LP-11.

This would be simpler and would work whatever the pre_enable order.

But this won't work for the tc358767, except if we add a dummy DSI host command
which powers up the DSI link.

This won't fix the PS8640 either who also needs a disabled DSI link to initialize.

Neil

>   
>   enum mipi_dsi_pixel_format {
>   	MIPI_DSI_FMT_RGB888,
> @@ -235,6 +251,11 @@ void mipi_dsi_device_unregister(struct mipi_dsi_device *dsi);
>   struct mipi_dsi_device *
>   devm_mipi_dsi_device_register_full(struct device *dev, struct mipi_dsi_host *host,
>   				   const struct mipi_dsi_device_info *info);
> +
> +bool mipi_dsi_host_power_control_available(struct mipi_dsi_host *host);
> +int mipi_dsi_host_power_up(struct mipi_dsi_host *host);
> +void mipi_dsi_host_power_down(struct mipi_dsi_host *host);
> +
>   struct mipi_dsi_device *of_find_mipi_dsi_device_by_node(struct device_node *np);
>   int mipi_dsi_attach(struct mipi_dsi_device *dsi);
>   int mipi_dsi_detach(struct mipi_dsi_device *dsi);