Re: [DPU PATCH 1/2] drm/msm/dsi: adjust dsi timing for dual dsi mode

[Sean Paul <seanpaul@chromium.org>]

On Tue, Apr 10, 2018 at 06:16:07PM -0700, Chandan Uddaraju wrote:
> For dual dsi mode, the horizontal timing needs
> to be divided by half since both the dsi controllers
> will be driving this panel. Adjust the pixel clock and
> DSI timing accordingly.
> 
> Change-Id: Iee1226b2eef9eea23d9653e3d738ee8cd2a2dd8e
> Signed-off-by: Chandan Uddaraju <chandanu@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/dsi/dsi.h         |  1 +
>  drivers/gpu/drm/msm/dsi/dsi_host.c    | 17 +++++++++++++++++
>  drivers/gpu/drm/msm/dsi/dsi_manager.c | 15 +++++++++++++++
>  3 files changed, 33 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi.h b/drivers/gpu/drm/msm/dsi/dsi.h
> index 70d9a9a..4131b47 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi.h
> +++ b/drivers/gpu/drm/msm/dsi/dsi.h
> @@ -161,6 +161,7 @@ void msm_dsi_host_cmd_xfer_commit(struct mipi_dsi_host *host,
>  					u32 dma_base, u32 len);
>  int msm_dsi_host_enable(struct mipi_dsi_host *host);
>  int msm_dsi_host_disable(struct mipi_dsi_host *host);
> +void msm_dsi_host_adjust_timing_config(struct mipi_dsi_host *host);
>  int msm_dsi_host_power_on(struct mipi_dsi_host *host,
>  			struct msm_dsi_phy_shared_timings *phy_shared_timings);
>  int msm_dsi_host_power_off(struct mipi_dsi_host *host);
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 7a03a94..66a21cb 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -2237,6 +2237,23 @@ static void msm_dsi_sfpb_config(struct msm_dsi_host *msm_host, bool enable)
>  			SFPB_GPREG_MASTER_PORT_EN(en));
>  }
>  
> +void msm_dsi_host_adjust_timing_config(struct mipi_dsi_host *host)
> +{
> +	struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
> +	struct drm_display_mode *mode = NULL;
> +
> +	mode = msm_host->mode;
> +
> +	mutex_lock(&msm_host->dev_mutex);
> +	mode->htotal >>= 1;
> +	mode->hdisplay >>= 1;
> +	mode->hsync_start >>= 1;
> +	mode->hsync_end >>= 1;
> +
> +	mode->clock >>= 1;

I don't think you should alter the mode. Instead, apply the division when you're
writing out to hardware. Also, no need to get fancy with a bitshift, just use /2
and trust that the compiler is smart :)

Sean

> +	mutex_unlock(&msm_host->dev_mutex);
> +}
> +
>  int msm_dsi_host_power_on(struct mipi_dsi_host *host,
>  			struct msm_dsi_phy_shared_timings *phy_shared_timings)
>  {
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> index 4cb1cb6..8ef1c3d 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> @@ -627,6 +627,21 @@ static void dsi_mgr_bridge_mode_set(struct drm_bridge *bridge,
>  	msm_dsi_host_set_display_mode(host, adjusted_mode);
>  	if (is_dual_dsi && other_dsi)
>  		msm_dsi_host_set_display_mode(other_dsi->host, adjusted_mode);
> +
> +	/*
> +	 * For dual DSI mode, the current DRM mode has
> +	 * the complete width of the panel. Since, the complete
> +	 * panel is driven by two DSI controllers, the
> +	 * horizontal timings and the pixel clock have to be
> +	 * split between the two dsi controllers. Adjust the
> +	 * DSI host timing structures accordingly.
> +	 */
> +	if (is_dual_dsi) {
> +		msm_dsi_host_adjust_timing_config(host);
> +		if (other_dsi)
> +			msm_dsi_host_adjust_timing_config(other_dsi->host);
> +	}
> +
>  }
>  
>  static const struct drm_connector_funcs dsi_mgr_connector_funcs = {
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS
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