Driver: Gx Chip

struct gx_mem_region phys_addr_t start; size_t size; void *cookie; struct list_head list; ; // Allocation from reserved CMA pool void *gx_mem_alloc(size_t size, u32 align); void gx_mem_free(void *handle);

Userspace (GStreamer V4L2) → ioctl(VIDIOC_QBUF) → driver copies bitstream to SRAM/CMA → triggers VPU via mailbox → VPU interrupts on frame done → driver queues decoded frame to capture buffer.

echo 0x1f > /sys/module/gx_vpu/parameters/debug to enable verbose logging. Check cat /proc/interrupts | grep vpu for interrupt count. 4.4 I2C / SPI Drivers ( gx_i2c , gx_spi ) These are simple wrapper drivers around DesignWare IP or a custom bit-bang. The GX implementation often lacks proper clock gating or recovery on bus hang. gx chip driver

If you can avoid GX for a new design, do so. If you're stuck, copy working register dumps from a known-good Android build and compare to your driver’s init sequence.

Example (display vsync):

writel_relaxed(val, i2c->base + reg);

can occur if status register is not cleared exactly once. 6. Debugging GX Drivers Without Vendor Support 6.1 Tools & Methods | Tool | Purpose | |------|---------| | devmem2 | Read/write raw registers (e.g., devmem2 0xF0000020 ) | | strace | Trace ioctl calls to DRM/V4L2 | | dmesg -w | Watch driver prints (enable with DYNAMIC_DEBUG ) | | cat /sys/kernel/debug/dri/*/state | DRM state | | gdb + KGDB | Kernel debugging over serial | 6.2 Common Errors & Fixes Error: gx_vpu: timeout waiting for interrupt → Check VPU clock (is it enabled?), firmware loaded? Try clk_enable(vpu_clk) . If you're stuck, copy working register dumps from

struct gx_disp *disp = dev_id; u32 status = readl(disp->base + DISP_IRQ_STS); if (status & DISP_IRQ_VSYNC) writel(DISP_IRQ_VSYNC, disp->base + DISP_IRQ_STS); drm_crtc_handle_vblank(&disp->crtc); return IRQ_HANDLED;

Manually gate unused clocks via /sys/kernel/debug/clk/clk_summary and write to clk_disable . reg = &lt

gx_mem: allocation failed (size=4194304) → Increase CMA size in bootargs: cma=384M or adjust per-pool sizes in device tree. 7. Device Tree Bindings (Example for GX350) &gx_vpu compatible = "nationalchip,gx350-vpu"; reg = <0x0 0xf1000000 0x0 0x4000>; interrupts = <0 33 4>; clocks = <&clkc GX350_CLK_VPU>, <&clkc GX350_CLK_VPU_AXI>; clock-names = "core", "bus"; firmware-name = "gx_vpu_fw.bin"; memory-region = <&vpu_mem>; ; &gx_disp compatible = "nationalchip,gx350-disp"; reg = <0x0 0xf0000000 0x0 0x2000>; interrupts = <0 25 4>; ports disp_out: endpoint remote-endpoint = <&hdmi_in>; ; ; ;