linux-kernel - Re: [PATCH 02/21] drm/msm/dsi: fix DSC width for the bonded DSI case

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Message-ID: <rspuwp3zpnzwfe26hv2yezy5ad5o7wliq7ucpobyaheytvcs3j@qtshf6cewb2f>
Date: Tue, 3 Sep 2024 11:50:34 +0200
From: Marijn Suijten <marijn.suijten@...ainline.org>
To: Jun Nie <jun.nie@...aro.org>
Cc: Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
	Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, Jonathan Marek <jonathan@...ek.ca>
Subject: Re: [PATCH 02/21] drm/msm/dsi: fix DSC width for the bonded DSI case

On 2024-08-29 18:17:31, Jun Nie wrote:
> From: Jonathan Marek <jonathan@...ek.ca>
> 
> For the bonded DSI case, DSC pic_width and timing calculations should use
> the width of a single panel instead of the total combined width.

When this patch was originally proposed we already discussed [1] that this is
**not** universally true.  On my hardware a single bonded panel always receives
the full width, at least on downstream kernels, and it works [2].

[1]: https://lore.kernel.org/linux-arm-msm/eanx45rnasj7lu3r2tfhtg4qkqkcidd6zctsz6ci6jlklu4fgi@3nf73w2ka4li/T/#u
[2]: https://gitlab.freedesktop.org/drm/msm/-/issues/41

Can we please figure this out before landing this patch?

- Marijn

> Bonded DSI can be used to drive a single panel having two input
> channels, or to drive two panels with a input channel on every panel that
> behave like single panel for display controller.
> 
> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> Signed-off-by: Jun Nie <jun.nie@...aro.org>
> ---
>  drivers/gpu/drm/msm/dsi/dsi.h         | 3 ++-
>  drivers/gpu/drm/msm/dsi/dsi_host.c    | 6 +++++-
>  drivers/gpu/drm/msm/dsi/dsi_manager.c | 2 +-
>  3 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi.h b/drivers/gpu/drm/msm/dsi/dsi.h
> index 87496db203d6c..35b90c462f637 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi.h
> +++ b/drivers/gpu/drm/msm/dsi/dsi.h
> @@ -79,7 +79,8 @@ int msm_dsi_host_power_off(struct mipi_dsi_host *host);
>  int msm_dsi_host_set_display_mode(struct mipi_dsi_host *host,
>  				  const struct drm_display_mode *mode);
>  enum drm_mode_status msm_dsi_host_check_dsc(struct mipi_dsi_host *host,
> -					    const struct drm_display_mode *mode);
> +					    const struct drm_display_mode *mode,
> +					    bool is_bonded_dsi);
>  unsigned long msm_dsi_host_get_mode_flags(struct mipi_dsi_host *host);
>  int msm_dsi_host_register(struct mipi_dsi_host *host);
>  void msm_dsi_host_unregister(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 6388bb12696ff..7a4d9c071be5a 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -2489,7 +2489,8 @@ int msm_dsi_host_set_display_mode(struct mipi_dsi_host *host,
>  }
>  
>  enum drm_mode_status msm_dsi_host_check_dsc(struct mipi_dsi_host *host,
> -					    const struct drm_display_mode *mode)
> +					    const struct drm_display_mode *mode,
> +					    bool is_bonded_dsi)
>  {
>  	struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
>  	struct drm_dsc_config *dsc = msm_host->dsc;
> @@ -2499,6 +2500,9 @@ enum drm_mode_status msm_dsi_host_check_dsc(struct mipi_dsi_host *host,
>  	if (!msm_host->dsc)
>  		return MODE_OK;
>  
> +	if (is_bonded_dsi)
> +		pic_width = mode->hdisplay / 2;
> +
>  	if (pic_width % dsc->slice_width) {
>  		pr_err("DSI: pic_width %d has to be multiple of slice %d\n",
>  		       pic_width, dsc->slice_width);
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> index a210b7c9e5ca2..6e915b57e14bb 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> @@ -420,7 +420,7 @@ static enum drm_mode_status dsi_mgr_bridge_mode_valid(struct drm_bridge *bridge,
>  			return MODE_ERROR;
>  	}
>  
> -	return msm_dsi_host_check_dsc(host, mode);
> +	return msm_dsi_host_check_dsc(host, mode, IS_BONDED_DSI());
>  }
>  
>  static int dsi_mgr_bridge_attach(struct drm_bridge *bridge,
> 
> -- 
> 2.34.1
>