linux-kernel - Re: [PATCH 3/3] drm/vc4: hdmi: Add pixel bvb clock control

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Date:   Thu, 27 Aug 2020 13:35:02 +0900
From:   Hoegeun Kwon <hoegeun.kwon@...sung.com>
To:     Stefan Wahren <stefan.wahren@...e.com>, nsaenzjulienne@...e.de,
        eric@...olt.net, maxime@...no.tech
Cc:     devicetree@...r.kernel.org, tim.gover@...pberrypi.com,
        kdasu.kdev@...il.com, sboyd@...nel.org, mturquette@...libre.com,
        dave.stevenson@...pberrypi.com, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, phil@...pberrypi.com,
        robh+dt@...nel.org, bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Hoegeun Kwon <hoegeun.kwon@...sung.com>
Subject: Re: [PATCH 3/3] drm/vc4: hdmi: Add pixel bvb clock control

Hi Stefan,

Thank you for your review.


On 8/26/20 7:04 PM, Stefan Wahren wrote:
> Hi Hoeguen,
>
> Am 21.08.20 um 09:10 schrieb Hoegeun Kwon:
>> 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.
> this patch introduces a mandatory clock, please update
> brcm,bcm2835-hdmi.yaml first.
>
> Is this clock physically available on BCM283x or only on BCM2711?

As far as I know, BCM2711 raspberry pi 4 supports 4k,

don't supported on pi 3 and pi 3+.

Since 4k is not supported in versions prior to Raspberry Pi 4,

I don't think we need to modify the bvb clock.


So I think it is better to update 'brcm,bcm2711-hdmi.yaml'

instead of 'brcm,bcm2835-hdmi.yaml'.

Please comment, what do you think?

>
> I'm a little bit afraid, this change could break with older firmware
> versions on BCM283x.

Tested it several times with libdrm modetest.

I expect there will be no problem.


Best regards,

Hoegeun

>
> Best regards
> Stefan
>
>> 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;
>> +	}
>> +
>>   	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;
>>   
>