linux-kernel - Re: [PATCH v4 03/78] drm/vc4: hvs: Boost the core clock during modeset

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Message-ID: <20200902144843.fuvgtu62wdrnd4on@gilmour.lan>
Date:   Wed, 2 Sep 2020 16:48:43 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Chanwoo Choi <cw00.choi@...sung.com>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Eric Anholt <eric@...olt.net>, dri-devel@...ts.freedesktop.org,
        linux-rpi-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH v4 03/78] drm/vc4: hvs: Boost the core clock during
 modeset

Hi,

On Tue, Sep 01, 2020 at 08:21:36PM +0900, 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@...olt.net>
> > Signed-off-by: Maxime Ripard <maxime@...no.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;
>  }

Good catch, thanks!
Maxime

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