Re: [PATCH v2] drm/bridge/synopsys: dsi: add optional pixel clock

[Philippe CORNU <philippe.cornu@st.com>]

Hi Andrzej,

On 01/15/2018 02:52 PM, Andrzej Hajda wrote:
> On 12.01.2018 17:25, Philippe Cornu wrote:
>> The pixel clock is optional. When available, it offers a better
>> preciseness for timing computations and allows to reduce the extra dsi
>> bandwidth in burst mode (from ~20% to ~10-12%, hw platform dependent).
>>
>> Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
>> ---
>> Changes in v2: Improve px_clk probing in case of ENOENT dt returned value
>> (thanks to Philipp Zabel & Andrzej Hajda comments)
>>
>>   drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 26 ++++++++++++++++++++------
>>   1 file changed, 20 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> index c39c7dce20ed..62fcff881b98 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> @@ -225,6 +225,7 @@ struct dw_mipi_dsi {
>>   	void __iomem *base;
>>   
>>   	struct clk *pclk;
>> +	struct clk *px_clk;
>>   
>>   	unsigned int lane_mbps; /* per lane */
>>   	u32 channel;
>> @@ -753,24 +754,28 @@ void dw_mipi_dsi_bridge_mode_set(struct drm_bridge *bridge,
>>   	struct dw_mipi_dsi *dsi = bridge_to_dsi(bridge);
>>   	const struct dw_mipi_dsi_phy_ops *phy_ops = dsi->plat_data->phy_ops;
>>   	void *priv_data = dsi->plat_data->priv_data;
>> +	struct drm_display_mode px_clk_mode = *mode;
>>   	int ret;
>>   
>>   	clk_prepare_enable(dsi->pclk);
>>   
>> -	ret = phy_ops->get_lane_mbps(priv_data, mode, dsi->mode_flags,
>> +	if (dsi->px_clk)
>> +		px_clk_mode.clock = clk_get_rate(dsi->px_clk) / 1000;
>> +
>> +	ret = phy_ops->get_lane_mbps(priv_data, &px_clk_mode, dsi->mode_flags,
>>   				     dsi->lanes, dsi->format, &dsi->lane_mbps);
>>   	if (ret)
>>   		DRM_DEBUG_DRIVER("Phy get_lane_mbps() failed\n");
>>   
>>   	pm_runtime_get_sync(dsi->dev);
>>   	dw_mipi_dsi_init(dsi);
>> -	dw_mipi_dsi_dpi_config(dsi, mode);
>> +	dw_mipi_dsi_dpi_config(dsi, &px_clk_mode);
>>   	dw_mipi_dsi_packet_handler_config(dsi);
>>   	dw_mipi_dsi_video_mode_config(dsi);
>> -	dw_mipi_dsi_video_packet_config(dsi, mode);
>> +	dw_mipi_dsi_video_packet_config(dsi, &px_clk_mode);
>>   	dw_mipi_dsi_command_mode_config(dsi);
>> -	dw_mipi_dsi_line_timer_config(dsi, mode);
>> -	dw_mipi_dsi_vertical_timing_config(dsi, mode);
>> +	dw_mipi_dsi_line_timer_config(dsi, &px_clk_mode);
>> +	dw_mipi_dsi_vertical_timing_config(dsi, &px_clk_mode);
>>   
>>   	dw_mipi_dsi_dphy_init(dsi);
>>   	dw_mipi_dsi_dphy_timing_config(dsi);
>> @@ -784,7 +789,7 @@ void dw_mipi_dsi_bridge_mode_set(struct drm_bridge *bridge,
>>   
>>   	dw_mipi_dsi_dphy_enable(dsi);
>>   
>> -	dw_mipi_dsi_wait_for_two_frames(mode);
>> +	dw_mipi_dsi_wait_for_two_frames(&px_clk_mode);
>>   
>>   	/* Switch to cmd mode for panel-bridge pre_enable & panel prepare */
>>   	dw_mipi_dsi_set_mode(dsi, 0);
>> @@ -878,6 +883,15 @@ __dw_mipi_dsi_probe(struct platform_device *pdev,
>>   		return ERR_PTR(ret);
>>   	}
>>   
>> +	dsi->px_clk = devm_clk_get(dev, "px_clk");
>> +	if (PTR_ERR(dsi->px_clk) == -ENOENT) {
>> +		dsi->px_clk = NULL;
>> +	} else if (IS_ERR(dsi->px_clk)) {
>> +		ret = PTR_ERR(dsi->px_clk);
>> +		dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
>> +		dsi->px_clk = NULL;
>> +	}
>> +
> As I understand on fail you just log an error and continue?
> The code could be slightly simplified, for example:
> dsi->px_clk = devm_clk_get(dev, "px_clk");
> if (IS_ERR(dsi->px_clk)) {
>          ret = PTR_ERR(dsi->px_clk);
>          if (ret != ENOENT)
>                  dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
>          dsi->px_clk = NULL;
> }
> 
> With or without this change:
> 
> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
> 

Thanks for your review.

Yes in this version, on fail, I just log an error and continue, 
especially because this px_clk is "optional" in the documentation. Then 
your proposal is much better than mine : )

Nevertheless, I wonder now if it could be better to "return" in case of 
error as we do for others mandatory clocks...
So then, the code could be:

dsi->px_clk = devm_clk_get(dev, "px_clk");
if (IS_ERR(dsi->px_clk)) {
	dsi->px_clk = NULL;
	ret = PTR_ERR(dsi->px_clk);
	if (ret != ENOENT) {
		dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
		return ERR_PTR(ret);
	}
}


Do you (or someone else) have a preferred choice?


Many thanks,
Philippe :-)

>   --
> Regards
> Andrzej
> 
> 
>>   	/*
>>   	 * Note that the reset was not defined in the initial device tree, so
>>   	 * we have to be prepared for it not being found.
> 
>