linux-kernel - Re: [PATCH v2 2/4] drm/vc4: hdmi: Add pixel bvb clock control

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Message-ID: <46e051f7-ba72-5960-da95-a2e9c44d2d85@samsung.com>
Date:   Tue, 1 Sep 2020 13:27:33 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Hoegeun Kwon <hoegeun.kwon@...sung.com>, nsaenzjulienne@...e.de,
        eric@...olt.net, maxime@...no.tech, stefan.wahren@...e.com,
        dave.stevenson@...pberrypi.com
Cc:     devicetree@...r.kernel.org, tim.gover@...pberrypi.com,
        sboyd@...nel.org, mturquette@...libre.com, kdasu.kdev@...il.com,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-clk@...r.kernel.org, robh+dt@...nel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org, phil@...pberrypi.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/4] drm/vc4: hdmi: Add pixel bvb clock control

Hi Hoegeun,

It looks good to me. But, just one comment.

On 9/1/20 1:07 PM, Hoegeun Kwon wrote:
> There is a problem that the output does not work at a resolution
> exceeding FHD. To solve this, we need to adjust the bvb clock at a
> resolution exceeding FHD.
> 
> Signed-off-by: Hoegeun Kwon <hoegeun.kwon@...sung.com>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 25 +++++++++++++++++++++++++
>  drivers/gpu/drm/vc4/vc4_hdmi.h |  1 +
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index 95ec5eedea39..eb3192d1fd86 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -80,6 +80,7 @@
>  # define VC4_HD_M_ENABLE			BIT(0)
>  
>  #define CEC_CLOCK_FREQ 40000
> +#define VC4_HSM_MID_CLOCK 149985000
>  
>  static int vc4_hdmi_debugfs_regs(struct seq_file *m, void *unused)
>  {
> @@ -380,6 +381,7 @@ static void vc4_hdmi_encoder_post_crtc_powerdown(struct drm_encoder *encoder)
>  	HDMI_WRITE(HDMI_VID_CTL,
>  		   HDMI_READ(HDMI_VID_CTL) & ~VC4_HD_VID_CTL_ENABLE);
>  
> +	clk_disable_unprepare(vc4_hdmi->pixel_bvb_clock);
>  	clk_disable_unprepare(vc4_hdmi->hsm_clock);
>  	clk_disable_unprepare(vc4_hdmi->pixel_clock);
>  
> @@ -638,6 +640,23 @@ static void vc4_hdmi_encoder_pre_crtc_configure(struct drm_encoder *encoder)
>  		return;
>  	}
>  
> +	ret = clk_set_rate(vc4_hdmi->pixel_bvb_clock,
> +			(hsm_rate > VC4_HSM_MID_CLOCK ? 150000000 : 75000000));
> +	if (ret) {
> +		DRM_ERROR("Failed to set pixel bvb clock rate: %d\n", ret);
> +		clk_disable_unprepare(vc4_hdmi->hsm_clock);
> +		clk_disable_unprepare(vc4_hdmi->pixel_clock);
> +		return;
> +	}
> +
> +	ret = clk_prepare_enable(vc4_hdmi->pixel_bvb_clock);
> +	if (ret) {
> +		DRM_ERROR("Failed to turn on pixel bvb clock: %d\n", ret);
> +		clk_disable_unprepare(vc4_hdmi->hsm_clock);
> +		clk_disable_unprepare(vc4_hdmi->pixel_clock);
> +		return;
> +	}

Generally, enable the clock before using clk and then change the clock rate.
I think that you better to change the order between clk_prepare_enable and clk_set_rate.


> +
>  	if (vc4_hdmi->variant->reset)
>  		vc4_hdmi->variant->reset(vc4_hdmi);
>  
> @@ -1593,6 +1612,12 @@ static int vc5_hdmi_init_resources(struct vc4_hdmi *vc4_hdmi)
>  		return PTR_ERR(vc4_hdmi->audio_clock);
>  	}
>  
> +	vc4_hdmi->pixel_bvb_clock = devm_clk_get(dev, "bvb");
> +	if (IS_ERR(vc4_hdmi->pixel_bvb_clock)) {
> +		DRM_ERROR("Failed to get pixel bvb clock\n");
> +		return PTR_ERR(vc4_hdmi->pixel_bvb_clock);
> +	}
> +
>  	vc4_hdmi->reset = devm_reset_control_get(dev, NULL);
>  	if (IS_ERR(vc4_hdmi->reset)) {
>  		DRM_ERROR("Failed to get HDMI reset line\n");
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> index 0806c6d9f24e..63c6f8bddf1d 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> @@ -147,6 +147,7 @@ struct vc4_hdmi {
>  	struct clk *pixel_clock;
>  	struct clk *hsm_clock;
>  	struct clk *audio_clock;
> +	struct clk *pixel_bvb_clock;
>  
>  	struct reset_control *reset;
>  
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics