linux-kernel - Re: [PATCH RFC 02/21] media: cadence: csi2rx: configure DPHY before starting source stream

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Date: Thu, 22 Feb 2024 15:29:54 +0100
From: Julien Massot <julien.massot@...labora.com>
To: Jai Luthra <j-luthra@...com>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Hans Verkuil <hverkuil-cisco@...all.nl>, Vaishnav Achath
 <vaishnav.a@...com>, Maxime Ripard <mripard@...nel.org>,
 Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, Vignesh Raghavendra <vigneshr@...com>,
 Aradhya Bhatia <a-bhatia1@...com>, Devarsh Thakkar <devarsht@...com>,
 Changhuang Liang <changhuang.liang@...rfivetech.com>,
 Jack Zhu <jack.zhu@...rfivetech.com>, Jayshri Pawar <jpawar@...ence.com>
Subject: Re: [PATCH RFC 02/21] media: cadence: csi2rx: configure DPHY before
 starting source stream

Hi Jai,

On 2/22/24 12:31, Jai Luthra wrote:
> From: Pratyush Yadav <p.yadav@...com>
> 
> When the source device is operating above 1.5 Gbps per lane, it needs to
> send the Skew Calibration Sequence before sending any HS data. If the
> DPHY is initialized after the source stream is started, then it might
> miss the sequence and not be able to receive data properly. Move the
> start of source subdev to the end of the sequence to make sure
> everything is ready to receive data before the source starts streaming.
> 
> Signed-off-by: Pratyush Yadav <p.yadav@...com>
> Signed-off-by: Jai Luthra <j-luthra@...com>

Thanks for your patch!
This patch is useful even at lower data rate than 1.5 Gbps.
I'm having the issue at 800Mbps with max96714F deserializer.

Should this patch deserve a Fixes tag?
Fixes: 3295cf1241d3 ("media: cadence: Add support for external dphy")

Reviewed-by: Julien Massot <julien.massot@...labora.com>
Tested-by: Julien Massot <julien.massot@...labora.com>

> ---
>   drivers/media/platform/cadence/cdns-csi2rx.c | 26 ++++++++++++++------------
>   1 file changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/media/platform/cadence/cdns-csi2rx.c b/drivers/media/platform/cadence/cdns-csi2rx.c
> index 70b7f8a9e4f2..75e602c1d762 100644
> --- a/drivers/media/platform/cadence/cdns-csi2rx.c
> +++ b/drivers/media/platform/cadence/cdns-csi2rx.c
> @@ -243,10 +243,6 @@ static int csi2rx_start(struct csi2rx_priv *csi2rx)
>   
>   	writel(reg, csi2rx->base + CSI2RX_STATIC_CFG_REG);
>   
> -	ret = v4l2_subdev_call(csi2rx->source_subdev, video, s_stream, true);
> -	if (ret)
> -		goto err_disable_pclk;
> -
>   	/* Enable DPHY clk and data lanes. */
>   	if (csi2rx->dphy) {
>   		reg = CSI2RX_DPHY_CL_EN | CSI2RX_DPHY_CL_RST;
> @@ -256,6 +252,13 @@ static int csi2rx_start(struct csi2rx_priv *csi2rx)
>   		}
>   
>   		writel(reg, csi2rx->base + CSI2RX_DPHY_LANE_CTRL_REG);
> +
> +		ret = csi2rx_configure_ext_dphy(csi2rx);
> +		if (ret) {
> +			dev_err(csi2rx->dev,
> +				"Failed to configure external DPHY: %d\n", ret);
> +			goto err_disable_pclk;
> +		}
>   	}
>   
>   	/*
> @@ -295,14 +298,9 @@ static int csi2rx_start(struct csi2rx_priv *csi2rx)
>   
>   	reset_control_deassert(csi2rx->sys_rst);
>   
> -	if (csi2rx->dphy) {
> -		ret = csi2rx_configure_ext_dphy(csi2rx);
> -		if (ret) {
> -			dev_err(csi2rx->dev,
> -				"Failed to configure external DPHY: %d\n", ret);
> -			goto err_disable_sysclk;
> -		}
> -	}
> +	ret = v4l2_subdev_call(csi2rx->source_subdev, video, s_stream, true);
> +	if (ret)
> +		goto err_disable_sysclk;
>   
>   	clk_disable_unprepare(csi2rx->p_clk);
>   
> @@ -316,6 +314,10 @@ static int csi2rx_start(struct csi2rx_priv *csi2rx)
>   		clk_disable_unprepare(csi2rx->pixel_clk[i - 1]);
>   	}
>   
> +	if (csi2rx->dphy) {
> +		writel(0, csi2rx->base + CSI2RX_DPHY_LANE_CTRL_REG);
> +		phy_power_off(csi2rx->dphy);
> +	}
>   err_disable_pclk:
>   	clk_disable_unprepare(csi2rx->p_clk);
>   
> 

-- 
Julien Massot
Senior Software Engineer
Collabora Ltd.
Platinum Building, St John's Innovation Park, Cambridge CB4 0DS, UK
Registered in England & Wales, no. 5513718