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Subject: Re: [PATCH 3/3] drm/vc4: hdmi: Add pixel bvb clock control
To:     Stefan Wahren <stefan.wahren@i2se.com>, nsaenzjulienne@suse.de,
        eric@anholt.net, maxime@cerno.tech
Cc:     devicetree@vger.kernel.org, tim.gover@raspberrypi.com,
        dave.stevenson@raspberrypi.com, sboyd@kernel.org,
        mturquette@baylibre.com, kdasu.kdev@gmail.com,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-clk@vger.kernel.org, robh+dt@kernel.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-rpi-kernel@lists.infradead.org, phil@raspberrypi.com,
        linux-arm-kernel@lists.infradead.org,
        Hoegeun Kwon <hoegeun.kwon@samsung.com>
From:   Hoegeun Kwon <hoegeun.kwon@samsung.com>
Message-ID: <a19de8d5-2b01-cb62-38a2-b0732068025c@samsung.com>
Date:   Fri, 28 Aug 2020 15:30:04 +0900
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On 8/27/20 6:49 PM, Stefan Wahren wrote:
> Am 27.08.20 um 06:35 schrieb Hoegeun Kwon:
>> 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'.
> You are correct please update only brcm,bcm2711-hdmi.yaml.
>
> My concern was that the function vc4_hdmi_encoder_pre_crtc_configure()
> is called on a non-bcm2711 platform or on a Raspberry Pi 4 with an older
> DTB. So making the BVB clock optional might be better?

You are right, if use old dtb, we have a problem with the hdmi driver.

So how about modifying it like this?

@@ -1614,8 +1614,8 @@ static int vc5_hdmi_init_resources(struct vc4_hdmi 
*vc4_hdmi)

         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);
+               DRM_WARN("Failed to get pixel bvb clock\n");
+               vc4_hdmi->pixel_bvb_clock = NULL;
         }

         vc4_hdmi->reset = devm_reset_control_get(dev, NULL);

If we modify like this, if there is no bvb clock in dtb, then 
pixel_bvb_clock will be null

and it will not affect the clk control function below.

   - clk_set_rate()
   - clk_prepare_enable()
   - clk_disable_unprepare()


Best regards

Hoegeun

>
>> 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@samsung.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;
>>>>    
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>