Re: [PATCH 13/21] drm: mxsfb: Don't touch AXI clock in IRQ context

From: Stefan Agner <stefan@agner.ch>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Marek Vasut <marex@denx.de>,
	kernel@pengutronix.de, dri-devel@lists.freedesktop.org,
	linux-imx@nxp.com
Subject: Re: [PATCH 13/21] drm: mxsfb: Don't touch AXI clock in IRQ context
Date: Mon, 23 Mar 2020 23:50:29 +0100	[thread overview]
Message-ID: <e4cac7a95851cc62c762cf887d0ad691@agner.ch> (raw)
In-Reply-To: <20200309195216.31042-14-laurent.pinchart@ideasonboard.com>

On 2020-03-09 20:52, Laurent Pinchart wrote:
> The driver attempts agressive power management by enabling and disabling
> the AXI clock around register accesses. This results in attempts to
> enable and disable the clock in the IRQ handler, which is a no-go as
> preparing or unpreparing the clock may sleep.
> 
> On the other hand, the driver enables the AXI clock when enabling the
> CRTC and keeps it enabled until the CRTC is disabled. This is correct,
> and renders the power management attempt pointless, as interrupts are
> not supposed to occur when the CRTC is off.
> 
> The same reasoning can be applied to the CRTC .enable_vblank() and
> .disable_vblank() that are not supposed to be called when the CRTC off
> and thus don't require manual handling of the AXI clock. Furthermore,
> vblank handling is never enabled, which results in the vblank enable and
> disable handlers never being called.
> 
> To fix this, remove the manual clock handling in the IRQ, the CRTC
> .enable_vblank() and .disable_vblank() handlers and the plane
> .atomic_update() handler. We however need to handle the clock manually
> in mxsfb_irq_disable() as is calls .disable_vblank() manually and is
> used both at probe and remove time.
> 
> The clock disabling is also moved to the last step of the
> mxsfb_crtc_atomic_disable() function, to prepare for enabling vblank
> handling.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Looks good to me!

Reviewed-by: Stefan Agner <stefan@agner.ch>

> ---
>  drivers/gpu/drm/mxsfb/mxsfb_drv.c |  6 ++----
>  drivers/gpu/drm/mxsfb/mxsfb_kms.c | 15 ++++-----------
>  2 files changed, 6 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> index a8da92976d13..e324bd2a63a5 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> @@ -231,7 +231,9 @@ static void mxsfb_irq_disable(struct drm_device *drm)
>  {
>  	struct mxsfb_drm_private *mxsfb = drm->dev_private;
>  
> +	mxsfb_enable_axi_clk(mxsfb);
>  	mxsfb->crtc.funcs->disable_vblank(&mxsfb->crtc);
> +	mxsfb_disable_axi_clk(mxsfb);
>  }
>  
>  static irqreturn_t mxsfb_irq_handler(int irq, void *data)
> @@ -240,8 +242,6 @@ static irqreturn_t mxsfb_irq_handler(int irq, void *data)
>  	struct mxsfb_drm_private *mxsfb = drm->dev_private;
>  	u32 reg;
>  
> -	mxsfb_enable_axi_clk(mxsfb);
> -
>  	reg = readl(mxsfb->base + LCDC_CTRL1);
>  
>  	if (reg & CTRL1_CUR_FRAME_DONE_IRQ)
> @@ -249,8 +249,6 @@ static irqreturn_t mxsfb_irq_handler(int irq, void *data)
>  
>  	writel(CTRL1_CUR_FRAME_DONE_IRQ, mxsfb->base + LCDC_CTRL1 + REG_CLR);
>  
> -	mxsfb_disable_axi_clk(mxsfb);
> -
>  	return IRQ_HANDLED;
>  }
>  
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index ebe0785694cb..ac2696c8483d 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -344,9 +344,6 @@ static void mxsfb_crtc_atomic_disable(struct drm_crtc *crtc,
>  	struct drm_pending_vblank_event *event;
>  
>  	mxsfb_disable_controller(mxsfb);
> -	mxsfb_disable_axi_clk(mxsfb);
> -
> -	pm_runtime_put_sync(drm->dev);
>  
>  	spin_lock_irq(&drm->event_lock);
>  	event = crtc->state->event;
> @@ -355,6 +352,9 @@ static void mxsfb_crtc_atomic_disable(struct drm_crtc *crtc,
>  		drm_crtc_send_vblank_event(crtc, event);
>  	}
>  	spin_unlock_irq(&drm->event_lock);
> +
> +	mxsfb_disable_axi_clk(mxsfb);
> +	pm_runtime_put_sync(drm->dev);
>  }
>  
>  static int mxsfb_crtc_enable_vblank(struct drm_crtc *crtc)
> @@ -362,10 +362,8 @@ static int mxsfb_crtc_enable_vblank(struct drm_crtc *crtc)
>  	struct mxsfb_drm_private *mxsfb = to_mxsfb_drm_private(crtc->dev);
>  
>  	/* Clear and enable VBLANK IRQ */
> -	mxsfb_enable_axi_clk(mxsfb);
>  	writel(CTRL1_CUR_FRAME_DONE_IRQ, mxsfb->base + LCDC_CTRL1 + REG_CLR);
>  	writel(CTRL1_CUR_FRAME_DONE_IRQ_EN, mxsfb->base + LCDC_CTRL1 + REG_SET);
> -	mxsfb_disable_axi_clk(mxsfb);
>  
>  	return 0;
>  }
> @@ -375,10 +373,8 @@ static void mxsfb_crtc_disable_vblank(struct
> drm_crtc *crtc)
>  	struct mxsfb_drm_private *mxsfb = to_mxsfb_drm_private(crtc->dev);
>  
>  	/* Disable and clear VBLANK IRQ */
> -	mxsfb_enable_axi_clk(mxsfb);
>  	writel(CTRL1_CUR_FRAME_DONE_IRQ_EN, mxsfb->base + LCDC_CTRL1 + REG_CLR);
>  	writel(CTRL1_CUR_FRAME_DONE_IRQ, mxsfb->base + LCDC_CTRL1 + REG_CLR);
> -	mxsfb_disable_axi_clk(mxsfb);
>  }
>  
>  static const struct drm_crtc_helper_funcs mxsfb_crtc_helper_funcs = {
> @@ -433,11 +429,8 @@ static void mxsfb_plane_atomic_update(struct
> drm_plane *plane,
>  	dma_addr_t paddr;
>  
>  	paddr = mxsfb_get_fb_paddr(mxsfb);
> -	if (paddr) {
> -		mxsfb_enable_axi_clk(mxsfb);
> +	if (paddr)
>  		writel(paddr, mxsfb->base + mxsfb->devdata->next_buf);
> -		mxsfb_disable_axi_clk(mxsfb);
> -	}
>  }
>  
>  static const struct drm_plane_helper_funcs mxsfb_plane_helper_funcs = {
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