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

[Boris BREZILLON <boris.brezillon@free-electrons.com>]

On Mon, 22 Sep 2014 16:43:31 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> 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.

By "This is the default mask" do you mean it shouldn't be called at
all ? Cause I ran into some trouble when not calling this in my
atmel-hlcdc driver.
Actually, in my case the platform device is created by the MFD core
which seems to let the coherent_dma_mask uninitialized.

Best Regards,

Boris


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com