linux-kernel - Re: [PATCH] drm/msm/dsi: Enable BURST_MODE for command mode for DSI 6G v1.3+

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Message-ID: <o57lsyxwzz5ihqlzq4ewnlnevj36rrq44ohyaxm3htnxzmomxn@fuv2sa5frph3>
Date:   Wed, 14 Jun 2023 11:43:27 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Jessica Zhang <quic_jesszhan@...cinc.com>
Cc:     Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, quic_abhinavk@...cinc.com,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dsi: Enable BURST_MODE for command mode for DSI
 6G v1.3+

On 2023-06-12 16:37:36, Jessica Zhang wrote:
> During a frame transfer in command mode, there could be frequent
> LP11 <-> HS transitions when multiple DCS commands are sent mid-frame or
> if the DSI controller is running on slow clock and is throttled. To
> minimize frame latency due to these transitions, it is recommended to
> send the frame in a single burst.
> 
> This feature is supported for DSI 6G 1.3 and above, thus enable burst
> mode if supported.
> 
> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 744f2398a6d6..8254b06dca85 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -994,6 +994,11 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>  		dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_TOTAL,
>  			DSI_CMD_MDP_STREAM0_TOTAL_H_TOTAL(hdisplay) |
>  			DSI_CMD_MDP_STREAM0_TOTAL_V_TOTAL(mode->vdisplay));
> +
> +		if (msm_host->cfg_hnd->major == MSM_DSI_VER_MAJOR_6G &&
> +				msm_host->cfg_hnd->minor >= MSM_DSI_6G_VER_MINOR_V1_3)
> +			dsi_write(msm_host, REG_DSI_CMD_MODE_MDP_CTRL2,
> +					DSI_CMD_MODE_MDP_CTRL2_BURST_MODE);

This is not part of the timing setup, and a similar BURST_MODE flag is
enabled for video-mode in dsi_ctrl_config() - should it be moved there?

(There is a dsi_sw_reset() in between the calls to dsi_timing_setup()
 and dsi_ctrl_cfg())

Note that that function sets up the CMD_CFG0 and CMD_CFG1 register, with
the former having a very similar layout to MDP_CTRL2... is there
documentation outlining the difference?

- Marijn

>  	}
>  }
>  
> 
> ---
> base-commit: dd969f852ba4c66938c71889e826aa8e5300d2f2
> change-id: 20230608-b4-add-burst-mode-a5bb144069fa
> 
> Best regards,
> -- 
> Jessica Zhang <quic_jesszhan@...cinc.com>
>