linux-kernel - Re: [PATCH v2 1/5] drm/msm/dsi: add support VBIF_CTRL

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Message-ID: <tu6aaz6whzkqz4at26o2h6pvcua53squfpgfmiw3i4qshojoij@2erqc3zmxmos>
Date: Thu, 20 Feb 2025 12:27:12 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jun Nie <jun.nie@...aro.org>
Cc: Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Krishna Manikandan <quic_mkrishn@...cinc.com>, linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	Jonathan Marek <jonathan@...ek.ca>
Subject: Re: [PATCH v2 1/5] drm/msm/dsi: add support VBIF_CTRL_PRIORITY to
 v2.8.0 controller

On Thu, Feb 20, 2025 at 06:07:52PM +0800, Jun Nie wrote:
> This change originates from the Qualcomm Android Linux driver. It is
> essential to support a dual-DSI configuration with two panels in
> some circumstances per testing. As the name suggests, this modification
> may enhance the bandwidth robustness of a bus.

Please start by describing the problem and the result of the changes.
Otherwise it reads as it "may enhance or may worsen" the robustness.

> 
> Co-developed-by: Jonathan Marek <jonathan@...ek.ca>
> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> Signed-off-by: Jun Nie <jun.nie@...aro.org>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 42e100a8adca09d7b55afce0e2553e76d898744f..f59c4cd6bc8cdb31c1302f8e3ff395486c0b4898 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -2238,13 +2238,23 @@ int msm_dsi_host_cmd_rx(struct mipi_dsi_host *host,
>  	return ret;
>  }
>  
> +#define DSI_VBIF_CTRL			(0x01CC - 4)
> +#define DSI_VBIF_CTRL_PRIORITY		0x07
> +
>  void msm_dsi_host_cmd_xfer_commit(struct mipi_dsi_host *host, u32 dma_base,
>  				  u32 len)
>  {
>  	struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
> +	const struct msm_dsi_cfg_handler *cfg_hnd = msm_host->cfg_hnd;
> +	u32 reg;
>  
>  	dsi_write(msm_host, REG_DSI_DMA_BASE, dma_base);
>  	dsi_write(msm_host, REG_DSI_DMA_LEN, len);
> +	if (cfg_hnd->minor >= MSM_DSI_6G_VER_MINOR_V2_8_0) {
> +		reg = dsi_read(msm_host, DSI_VBIF_CTRL);
> +		reg |= (DSI_VBIF_CTRL_PRIORITY & 0x7);
> +		dsi_write(msm_host, DSI_VBIF_CTRL, reg);
> +	}
>  	dsi_write(msm_host, REG_DSI_TRIG_DMA, 1);
>  
>  	/* Make sure trigger happens */
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry