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Subject: Re: [PATCH v4 03/78] drm/vc4: hvs: Boost the core clock during
 modeset
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>
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <a4f6ea62-441a-8e5b-5383-13d7f2b1a920@samsung.com>
Date:   Tue, 1 Sep 2020 20:21:36 +0900
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Sender: linux-kernel-owner@vger.kernel.org
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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);
+
        vc4->hvs = NULL;
 }


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics