The Versatile Express has 8 MB of dedicated video RAM (VRAM) on the motherboard, which is what we should be using for the PL111 if available. On this platform, the memory backplane is constructed so that only this memory will work properly with the CLCD on the motherboard, using any other memory region just gives random snow on the display.
The CA9 Versatile Express also has a PL111 instance on its core tile. This is OK, it has been tested with the motherboard VRAM and that works just as fine as regular CMA memory.
The memory is assigned to the device using the memory-region device tree property and a "shared-dma-pool" reserved memory pool like this:
reserved-memory { #address-cells = <1>; #size-cells = <1>; ranges;
vram: vram@48000000 { compatible = "shared-dma-pool"; reg = <0x48000000 0x00800000>; no-map; }; };
clcd@1f000 { compatible = "arm,pl111", "arm,primecell"; (...) memory-region = <&vram>; }·;
Cc: Liviu Dudau liviu.dudau@arm.com Cc: Mali DP Maintainers malidp@foss.arm.com Signed-off-by: Linus Walleij linus.walleij@linaro.org --- drivers/gpu/drm/pl111/pl111_drv.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/gpu/drm/pl111/pl111_drv.c b/drivers/gpu/drm/pl111/pl111_drv.c index b469aa317d9d..e301f2a719a3 100644 --- a/drivers/gpu/drm/pl111/pl111_drv.c +++ b/drivers/gpu/drm/pl111/pl111_drv.c @@ -60,6 +60,7 @@ #include <linux/slab.h> #include <linux/of.h> #include <linux/of_graph.h> +#include <linux/of_reserved_mem.h>
#include <drm/drmP.h> #include <drm/drm_atomic_helper.h> @@ -262,6 +263,10 @@ static int pl111_amba_probe(struct amba_device *amba_dev, drm->dev_private = priv; priv->variant = variant;
+ ret = of_reserved_mem_device_init(dev); + if (!ret) + dev_info(dev, "using device-specific reserved memory\n"); + if (of_property_read_u32(dev->of_node, "max-memory-bandwidth", &priv->memory_bw)) { dev_info(dev, "no max memory bandwidth specified, assume unlimited\n");