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Subject: Re: [PATCH v4 03/78] drm/vc4: hvs: Boost the core clock during
 modeset
From:   Chanwoo Choi <cw00.choi@samsung.com>
To:     Maxime Ripard <maxime@cerno.tech>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Eric Anholt <eric@anholt.net>
Cc:     dri-devel@lists.freedesktop.org,
        linux-rpi-kernel@lists.infradead.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        Tim Gover <tim.gover@raspberrypi.com>,
        Phil Elwell <phil@raspberrypi.com>
Organization: Samsung Electronics
Message-ID: <6aa8ed4d-1457-ce27-f801-11a197088c56@samsung.com>
Date:   Tue, 1 Sep 2020 20:48:03 +0900
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On 9/1/20 8:21 PM, Chanwoo Choi wrote:
> Hi Maxime,
> 
> On 7/9/20 2:41 AM, Maxime Ripard wrote:
>> In order to prevent timeouts and stalls in the pipeline, the core clock
>> needs to be maxed at 500MHz during a modeset on the BCM2711.
>>
>> Reviewed-by: Eric Anholt <eric@anholt.net>
>> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
>> ---
>>  drivers/gpu/drm/vc4/vc4_drv.h |  2 ++
>>  drivers/gpu/drm/vc4/vc4_hvs.c |  9 +++++++++
>>  drivers/gpu/drm/vc4/vc4_kms.c |  9 +++++++++
>>  3 files changed, 20 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
>> index e4cde1f9224b..6358f6ca8d56 100644
>> --- a/drivers/gpu/drm/vc4/vc4_drv.h
>> +++ b/drivers/gpu/drm/vc4/vc4_drv.h
>> @@ -320,6 +320,8 @@ struct vc4_hvs {
>>  	void __iomem *regs;
>>  	u32 __iomem *dlist;
>>  
>> +	struct clk *core_clk;
>> +
>>  	/* Memory manager for CRTCs to allocate space in the display
>>  	 * list.  Units are dwords.
>>  	 */
>> diff --git a/drivers/gpu/drm/vc4/vc4_hvs.c b/drivers/gpu/drm/vc4/vc4_hvs.c
>> index 836d8799d79e..091fdf4908aa 100644
>> --- a/drivers/gpu/drm/vc4/vc4_hvs.c
>> +++ b/drivers/gpu/drm/vc4/vc4_hvs.c
>> @@ -19,6 +19,7 @@
>>   * each CRTC.
>>   */
>>  
>> +#include <linux/clk.h>
>>  #include <linux/component.h>
>>  #include <linux/platform_device.h>
>>  
>> @@ -540,6 +541,14 @@ static int vc4_hvs_bind(struct device *dev, struct device *master, void *data)
>>  	hvs->regset.regs = hvs_regs;
>>  	hvs->regset.nregs = ARRAY_SIZE(hvs_regs);
>>  
>> +	if (hvs->hvs5) {
>> +		hvs->core_clk = devm_clk_get(&pdev->dev, NULL);
>> +		if (IS_ERR(hvs->core_clk)) {
>> +			dev_err(&pdev->dev, "Couldn't get core clock\n");
>> +			return PTR_ERR(hvs->core_clk);
>> +		}
>> +	}
>> +
>>  	if (!hvs->hvs5)
>>  		hvs->dlist = hvs->regs + SCALER_DLIST_START;
>>  	else
>> diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
>> index 08318e69061b..210cc2408087 100644
>> --- a/drivers/gpu/drm/vc4/vc4_kms.c
>> +++ b/drivers/gpu/drm/vc4/vc4_kms.c
>> @@ -11,6 +11,8 @@
>>   * crtc, HDMI encoder).
>>   */
>>  
>> +#include <linux/clk.h>
>> +
>>  #include <drm/drm_atomic.h>
>>  #include <drm/drm_atomic_helper.h>
>>  #include <drm/drm_crtc.h>
>> @@ -149,6 +151,7 @@ vc4_atomic_complete_commit(struct drm_atomic_state *state)
>>  {
>>  	struct drm_device *dev = state->dev;
>>  	struct vc4_dev *vc4 = to_vc4_dev(dev);
>> +	struct vc4_hvs *hvs = vc4->hvs;
>>  	struct vc4_crtc *vc4_crtc;
>>  	int i;
>>  
>> @@ -160,6 +163,9 @@ vc4_atomic_complete_commit(struct drm_atomic_state *state)
>>  		vc4_hvs_mask_underrun(dev, vc4_crtc->channel);
>>  	}
>>  
>> +	if (vc4->hvs->hvs5)
>> +		clk_set_min_rate(hvs->core_clk, 500000000);
>> +
>>  	drm_atomic_helper_wait_for_fences(dev, state, false);
>>  
>>  	drm_atomic_helper_wait_for_dependencies(state);
>> @@ -182,6 +188,9 @@ vc4_atomic_complete_commit(struct drm_atomic_state *state)
>>  
>>  	drm_atomic_helper_commit_cleanup_done(state);
>>  
>> +	if (vc4->hvs->hvs5)
>> +		clk_set_min_rate(hvs->core_clk, 0);
>> +
>>  	drm_atomic_state_put(state);
>>  
>>  	up(&vc4->async_modeset);
>>
> 
> This patch doesn't control the enable/disable of core_clk.
> So, I think that it need to handle the clock as following:
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_hvs.c b/drivers/gpu/drm/vc4/vc4_hvs.c
> index 4ef88c0b51ab..355d67fd8beb 100644
> --- a/drivers/gpu/drm/vc4/vc4_hvs.c
> +++ b/drivers/gpu/drm/vc4/vc4_hvs.c
> @@ -588,6 +588,12 @@ static int vc4_hvs_bind(struct device *dev, struct device *master, void *data)
>                         dev_err(&pdev->dev, "Couldn't get core clock\n");
>                         return PTR_ERR(hvs->core_clk);
>                 }
> +
> +               ret = clk_prepare_enable(hvs->core_clk);
> +               if (ret) {
> +                       dev_err(&pdev->dev, "Couldn't enable core clock\n");
> +                       return ret;
> +               }
>         }
>  
>         if (!hvs->hvs5)
> @@ -681,6 +687,8 @@ static void vc4_hvs_unbind(struct device *dev, struct device *master,
>         drm_mm_takedown(&vc4->hvs->dlist_mm);
>         drm_mm_takedown(&vc4->hvs->lbm_mm);
>  
> +       clk_prepare_enable(vc4->hvs->core_clk);

I'm sorry. Change to clk_disable_unprepare(vc4->hvs->core_clk);

> +
>         vc4->hvs = NULL;
>  }
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics