linux-kernel - Re: [PATCH v4 1/5] drm/rockchip: Add basic drm driver

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Message-ID: <3036415.u40f3Xnhod@wuerfel>
Date:	Mon, 22 Sep 2014 16:43:31 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Mark yao <mark.yao@...k-chips.com>
Cc:	heiko@...ech.de,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	David Airlie <airlied@...il.com>,
	Rob Clark <robdclark@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Grant Likely <grant.likely@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	John Stultz <john.stultz@...aro.org>,
	Rom Lemarchand <romlem@...gle.com>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-api@...r.kernel.org,
	linux-rockchip@...ts.infradead.org, dianders@...omium.org,
	marcheu@...omium.org, dbehr@...omium.org, olof@...om.net,
	djkurtz@...omium.org, xjq@...k-chips.com, kfx@...k-chips.com,
	cym@...k-chips.com, cf@...k-chips.com, zyw@...k-chips.com,
	xxm@...k-chips.com, huangtao@...k-chips.com,
	kever.yang@...k-chips.com, yxj@...k-chips.com, wxt@...k-chips.com,
	xw@...k-chips.com
Subject: Re: [PATCH v4 1/5] drm/rockchip: Add basic drm driver

On Monday 22 September 2014 18:48:54 Mark yao wrote:
> diff --git a/drivers/gpu/drm/rockchip/Kconfig b/drivers/gpu/drm/rockchip/Kconfig
> new file mode 100644
> index 0000000..7146c80
> --- /dev/null
> +++ b/drivers/gpu/drm/rockchip/Kconfig
> @@ -0,0 +1,19 @@
> +config DRM_ROCKCHIP
> +	tristate "DRM Support for Rockchip"
> +	depends on DRM && ROCKCHIP_IOMMU
> +	select ARM_DMA_USE_IOMMU
> +	select IOMMU_API
> +	select DRM_KMS_HELPER
> +	select DRM_KMS_FB_HELPER
> +	select DRM_PANEL
> +	select FB_CFB_FILLRECT
> +	select FB_CFB_COPYAREA
> +	select FB_CFB_IMAGEBLIT
> +	select VT_HW_CONSOLE_BINDING if FRAMEBUFFER_CONSOLE
> +	select VIDEOMODE_HELPERS

Be careful with 'select', at least some of these should be 'depends on'.
In particular IOMMU_API and ARM_DMA_USE_IOMMU, but possibly others
as well. Just check how the symbols are used normally, if you get this
wrong, we can end up with incorrect dependencies or loops.

> diff --git a/drivers/gpu/drm/rockchip/Makefile b/drivers/gpu/drm/rockchip/Makefile
> new file mode 100644
> index 0000000..6e6d468
> --- /dev/null
> +++ b/drivers/gpu/drm/rockchip/Makefile
> @@ -0,0 +1,10 @@
> +#
> +# Makefile for the drm device driver.  This driver provides support for the
> +# Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
> +
> +ccflags-y := -Iinclude/drm -Idrivers/gpu/drm/rockchip

The second one should not be required.

> +static int rockchip_drm_load(struct drm_device *drm_dev, unsigned long flags)
> +{
> +	struct rockchip_drm_private *private;
> +	struct dma_iommu_mapping *mapping;
> +	struct device *dev = drm_dev->dev;
> +	int ret;
> +
> +	private = devm_kzalloc(drm_dev->dev, sizeof(*private), GFP_KERNEL);
> +	if (!private)
> +		return -ENOMEM;
> +
> +	dev_set_drvdata(drm_dev->dev, dev);
> +	drm_dev->dev_private = private;
> +
> +	drm_mode_config_init(drm_dev);
> +
> +	rockchip_drm_mode_config_init(drm_dev);
> +
> +	dev->dma_parms = devm_kzalloc(dev, sizeof(*dev->dma_parms),
> +				      GFP_KERNEL);
> +	if (!dev->dma_parms) {
> +		ret = -ENOMEM;
> +		goto err_config_cleanup;
> +	}
> +
> +	/* TODO(djkurtz): fetch the mapping start/size from somewhere */
> +	mapping = arm_iommu_create_mapping(&platform_bus_type, 0x10000000,
> +					   SZ_1G);
> +	if (IS_ERR(mapping)) {
> +		ret = PTR_ERR(mapping);
> +		goto err_config_cleanup;
> +	}
> +
> +	dma_set_coherent_mask(dev, DMA_BIT_MASK(32));

This is the default coherent mask. If you call this function, you
should normally check the return value, or call dma_set_mask first,
which you apparently don't do here, and in another place in this
patch.

	Arnd
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