[PATCH v5 06/29] drm/omap: dsi: send nop instead of page & column

[Sebastian Reichel]

Hi,

On Tue, Dec 08, 2020 at 02:28:32PM +0200, Tomi Valkeinen wrote:
> The OMAP DSI command mode panel driver used to send page & column
> address before each frame update, and this code was moved into the DSI
> host driver when converting it to the DRM bridge model.
> 
> However, it's not really required to send the page & column address
> before each frame. It's also something that doesn't really belong to the
> DSI host driver, so we should drop the code.
> 
> That said, frame updates break if we don't send _something_ between the
> frames. A NOP command does the trick.
> 
> It is not clear if this behavior is as expected from a DSI command mode
> frame transfer, or is it a feature/issue with OMAP DSI driver, or a
> feature/issue in the command mode panel used.
> 
> Most likely this is related to the following from the DSI spec:
> 
> "To enable PHY synchronization the host processor should periodically
> end HS transmission and drive the Data Lanes to the LP state. This
> transition should take place at least once per frame."
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---

Reviewed-by: Sebastian Reichel <sebastian.reichel at collabora.com>

-- Sebastian

>  drivers/gpu/drm/omapdrm/dss/dsi.c | 46 ++++++++++++-------------------
>  1 file changed, 17 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
> index 7fee9cf8782d..c6e044f8bece 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
> @@ -3884,35 +3884,19 @@ static int _dsi_update(struct dsi_data *dsi)
>  	return 0;
>  }
>  
> -static int _dsi_update_window(struct dsi_data *dsi, int channel,
> -			      int x, int y, int w, int h)
> -{
> -	int x1 = x, x2 = (x + w - 1);
> -	int y1 = y, y2 = (y + h - 1);
> -	u8 payloadX[5] = { MIPI_DCS_SET_COLUMN_ADDRESS,
> -			   x1 >> 8, x1 & 0xff, x2 >> 8, x2 & 0xff };
> -	u8 payloadY[5] = { MIPI_DCS_SET_PAGE_ADDRESS,
> -			   y1 >> 8, y1 & 0xff, y2 >> 8, y2 & 0xff };
> -	struct mipi_dsi_msg msgX = { 0 }, msgY = { 0 };
> -	int ret;
> +static int _dsi_send_nop(struct dsi_data *dsi, int channel)
> +{
> +	const u8 payload[] = { MIPI_DCS_NOP };
> +	const struct mipi_dsi_msg msg = {
> +		.channel = channel,
> +		.type = MIPI_DSI_DCS_SHORT_WRITE,
> +		.tx_len = 1,
> +		.tx_buf = payload,
> +	};
>  
>  	WARN_ON(!dsi_bus_is_locked(dsi));
>  
> -	msgX.type = MIPI_DSI_DCS_LONG_WRITE;
> -	msgX.channel = channel;
> -	msgX.tx_buf = payloadX;
> -	msgX.tx_len = sizeof(payloadX);
> -
> -	msgY.type = MIPI_DSI_DCS_LONG_WRITE;
> -	msgY.channel = channel;
> -	msgY.tx_buf = payloadY;
> -	msgY.tx_len = sizeof(payloadY);
> -
> -	ret = _omap_dsi_host_transfer(dsi, &msgX);
> -	if (ret != 0)
> -		return ret;
> -
> -	return _omap_dsi_host_transfer(dsi, &msgY);
> +	return _omap_dsi_host_transfer(dsi, &msg);
>  }
>  
>  static int dsi_update_channel(struct omap_dss_device *dssdev, int channel)
> @@ -3944,10 +3928,14 @@ static int dsi_update_channel(struct omap_dss_device *dssdev, int channel)
>  
>  	dsi_set_ulps_auto(dsi, false);
>  
> -	r = _dsi_update_window(dsi, channel, 0, 0, dsi->vm.hactive,
> -			       dsi->vm.vactive);
> +	/*
> +	 * Send NOP between the frames. If we don't send something here, the
> +	 * updates stop working. This is probably related to DSI spec stating
> +	 * that the DSI host should transition to LP at least once per frame.
> +	 */
> +	r = _dsi_send_nop(dsi, channel);
>  	if (r < 0) {
> -		DSSWARN("window update error: %d\n", r);
> +		DSSWARN("failed to send nop between frames: %d\n", r);
>  		goto err;
>  	}
>  
> -- 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> 
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