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

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

Hi Brian,

On 01/15/2018 06:11 PM, Andrzej Hajda wrote:
> On 15.01.2018 15:40, Philippe CORNU wrote:
>> 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?
> 
> No strong feelings, but I would slightly prefer current version: error
> is reported but the driver tries to do the best to continue work.
> On the other side it increases risk that the error will be ignored and
> potential bug not fixed.
> Choice between robustness and strictness.
> 
> Regards
> Andrzej

Before sending a v3 with Andrzej comments, may I ask you please to do a 
short review of this patch, particularly the 
dw_mipi_dsi_bridge_mode_set() function with the use of the optional 
pixel clock.

Many thanks for your support,
Philippe :-)

> 
>>
>>
>> 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.
> 
>