linux-kernel - Re: [PATCH v2 13/26] drm/fb_cma_helper: Remove implicit call to disable_unused

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Date:	Fri, 15 Jan 2016 01:13:05 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Mike Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	David Airlie <airlied@...ux.ie>,
	Thierry Reding <thierry.reding@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-sunxi@...glegroups.com,
	Chen-Yu Tsai <wens@...e.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Alexander Kaplan <alex@...tthing.co>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Wynter Woods <wynter@...tthing.co>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Rob Clark <robdclark@...il.com>,
	Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v2 13/26] drm/fb_cma_helper: Remove implicit call to disable_unused_functions

Hi Maxime,

Thank you for the patch.

On Thursday 14 January 2016 16:24:56 Maxime Ripard wrote:
> The drm_fbdev_cma_init function always calls the
> drm_helper_disable_unused_functions. Since it's part of the usual probe
> process, all the drivers using that helper will end up having their encoder
> and CRTC disable functions called at probe if their device has not been
> reported as enabled.
> 
> This could be fixed by reading out from the registers the current state of
> the device if it is enabled, but even that will not handle the case where
> the device is actually disabled.
> 
> Moreover, the drivers using the atomic modesetting expect that their enable
> and disable callback to be called when the device is already enabled or
> disabled (respectively).
> 
> We can however fix this issue by moving the call to
> drm_helper_disable_unused_functions out of drm_fbdev_cma_init and make the
> drivers needing it (all the drivers calling drm_fbdev_cma_init and not
> using the atomic modesetting) explicitly call it.

I'd rather add it to all drivers that call drm_fbdev_cma_init(). All the 
atomic ones must have special code to cope with it that could be rendered 
useless by the removal of the drm_helper_disable_unused_functions() call. That 
code should be removed too, and it would be easier to check drivers one by one 
and fixing them individually (outside of this patch series, unless you insist 
;-)) when removing the explicit drm_helper_disable_unused_functions() call. 
Other than that the patch looks fine to me.

> Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> ---
>  drivers/gpu/drm/drm_fb_cma_helper.c | 3 ---
>  drivers/gpu/drm/imx/imx-drm-core.c  | 1 +
>  drivers/gpu/drm/sti/sti_drv.c       | 1 +
>  drivers/gpu/drm/tilcdc/tilcdc_drv.c | 1 +
>  4 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c
> b/drivers/gpu/drm/drm_fb_cma_helper.c index c19a62561183..daa98d881142
> 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -348,9 +348,6 @@ struct drm_fbdev_cma *drm_fbdev_cma_init(struct
> drm_device *dev,
> 
>  	}
> 
> -	/* disable all the possible outputs/crtcs before entering KMS mode */
> -	drm_helper_disable_unused_functions(dev);
> -
>  	ret = drm_fb_helper_initial_config(helper, preferred_bpp);
>  	if (ret < 0) {
>  		dev_err(dev->dev, "Failed to set initial hw configuration.\n");
> diff --git a/drivers/gpu/drm/imx/imx-drm-core.c
> b/drivers/gpu/drm/imx/imx-drm-core.c index 7b990b4e96d2..e1db57791fc9
> 100644
> --- a/drivers/gpu/drm/imx/imx-drm-core.c
> +++ b/drivers/gpu/drm/imx/imx-drm-core.c
> @@ -312,6 +312,7 @@ static int imx_drm_driver_load(struct drm_device *drm,
> unsigned long flags) dev_warn(drm->dev, "Invalid legacyfb_depth. 
> Defaulting to 16bpp\n"); legacyfb_depth = 16;
>  	}
> +	drm_helper_disable_unused_functions(drm);
>  	imxdrm->fbhelper = drm_fbdev_cma_init(drm, legacyfb_depth,
>  				drm->mode_config.num_crtc, MAX_CRTC);
>  	if (IS_ERR(imxdrm->fbhelper)) {
> diff --git a/drivers/gpu/drm/sti/sti_drv.c b/drivers/gpu/drm/sti/sti_drv.c
> index 1469987949d8..506b5626f3ed 100644
> --- a/drivers/gpu/drm/sti/sti_drv.c
> +++ b/drivers/gpu/drm/sti/sti_drv.c
> @@ -160,6 +160,7 @@ static int sti_load(struct drm_device *dev, unsigned
> long flags)
> 
>  	drm_mode_config_reset(dev);
> 
> +	drm_helper_disable_unused_functions(dev);
>  	drm_fbdev_cma_init(dev, 32,
>  			   dev->mode_config.num_crtc,
>  			   dev->mode_config.num_connector);
> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
> b/drivers/gpu/drm/tilcdc/tilcdc_drv.c index 876cad58b1f9..24be31d69701
> 100644
> --- a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
> @@ -294,6 +294,7 @@ static int tilcdc_load(struct drm_device *dev, unsigned
> long flags) break;
>  	}
> 
> +	drm_helper_disable_unused_functions(dev);
>  	priv->fbdev = drm_fbdev_cma_init(dev, bpp,
>  			dev->mode_config.num_crtc,
>  			dev->mode_config.num_connector);

-- 
Regards,

Laurent Pinchart