Embedded Software Lab. @ SKKU 49 1 Sungkyunkwan University Tizen Linux Kernel.

Embedded Software Lab. @ SKKU

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Sungkyunkwan University

Tizen Linux Kernel


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• Memory Management– CMA (Contiguous Memory Allocator), IOMMU,

dma_buf, DRM (Direct Rendering Manager)• ARM Linux has no DMA_ZONE on buddy• Some devices require physically contiguous memory

(CMA), other devices has IOMMU thus be able to use non-contiguous memory

• Sharing DMA memory buffer for D/D to user

– Power management (CPUfreq, Devfreq, PM-QoS, Charger-manager)

– KDBUS– V4L2 (Video for Linux 2)– EXTCON

Tizen Kernel Additional features


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• Linux 3.0.15– Obsolete LTS (Current: 3.4 & 3.10)

• Support RD-PQ (Tizen 2) & RD-210 (tizen 1 & 2)– RD-PQ: Exynos4412– RD-210: Exynos 4210 (Linux 2.6.36 for Tizen 1)

• Not Good as Reference– Too many backported features.– Too OLD! No LTS/LTSI support– Many kernel hacks & dirty patches– git history removed.

• Forked from production kernel.• Hard to read

Previous Reference Kernel


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• Two reference kernels: ARM/Intel

• ARM (armv7, aarch64)– Linux 3.10.y

• 3.10.33 @ 2014/05• Full git history

– Armv6 support (Raspberry Pi) Coming soon.– Test & validation phase (integration test with

userspace)

• Intel (x86, x86_64)– Linux 3.14.1– Recent ATOM Soc support merged

Status of Tizen Reference Kernels


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5Tizen Kernel Overview


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6Tizen Kernel Overview (cont)


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Tizen Memory Management


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• Coupled with Graphics & Multimedia devices– Graphics & Multimedia devices = DMA devices

with HUGE Buffers

Tizen Memory Management


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• DRM is not Digital Right Management

• Direct Rendering Manager– Kernel-level graphics device driver that support

Direct Rendering Infrastructure.– Direct Rendering

• An application communicates directly with graphics device driver

– Display mode setting– Graphics memory management

What is DRM


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• Can give display experiences similar to PC environment.

• Why not use DRM until now?– DRM was designed for PC– Embedded System

• Low performance• No dedicated graphics memory• Not one graphics card but separated hardware

devices

– Linux frame buffer driver

Why DRM


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• Changed embedded environment– Powerful embedded SoCs– Requirements

• Display hotplug & clone, exteded mode• Unified memory management• Direct rendering• Varying device control with common interface

Why DRM (cont)


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• Currently, DRM support is only for Exynos SoCs. (ARM based)– Need Exynos specific DRM driver

• Exynos DRM driver– To support graphics hardware of Exynos SoCs– First ARM SoC graphics driver to use the DRM– Merged into the mainline linux 3.2 kernel– linux/drivers/gpu/drm/exynos

DRM of Tizen kernel


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• Graphics:– DRM (Direct Rendering Manager) / GEM

(Graphics Execution Manager)

Graphics (DRM / GEM)

GEM•Framework developed by Intel

• To manage graphics memory•Framework for buffer management

• Allocation and sharing


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GEM Allocation steps @ Tizen (Generic)

•DRM_IOCTL_MODE_CREATE_DUMB– Create GEM object(global) & user GEM handle(per process)

• dumb_create() of struct drm_driver– No physical memory allocated.

•DRM_IOCTL_MODE_MAP_DUMB– Create fake mmap offset of a gem object and relay the

object to user• A hash key of the gem object.• dumb_map_offset() of struct drm_driver

•MMAP– Request mmap based on the hash key as the offset– Create user address space– Setup cache attribute.– Not mapped to physical memory, yet

DRM / GEM Allocation


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GEM Allocation steps @ Tizen (Generic)

•On-demand Paging– Implement & Register a fault handler that

• With a page fault, allocate a page and map the page.

– vma->vm_ops->fault = xxx_drm_gem_fault

•Use!•DRM_IOCTL_MODE_DESTROY_DUMB– Remove GEM handle & object– Free memory– Implement dumb_destroy() of struct drm_driver

DRM / GEM Allocation (cont)


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GEM Allocation steps @ Tizen (Exynos Only)

•DRM_IOCTL_EXYNOS_GEM_CREATE– Only use user-desired size and buffer types.– Create gem object(global) & user gem handle(per

process)– physical memory allocated.

•DRM_IOCTL_EXYNOS_GEM_MMAP– Create user address space– Map the user address space to physical memory

•LIBDRM of Exynos uses these APIs, not the generic.

DRM / GEM Allocation (cont)


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GEM Sharing @ Tizen

•DRM_IOCTL_GEM_FLINK– “I will share this GEM to others.”– Create GEM object name for the given GEM handle

• Global key vaue for sharing

•DRM_IOCTL_GEM_OPEN– “I want to use the shared GEM.”– Create GEM handle based on the given GEM object

name

•DRM_IOCTL_GEM_CLOSE

DRM / GEM Sharing


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18Tizen Kernel MM –Multimedia (V4L2 / VB2)


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• Tizen recommends to use V4L2 at Tizen kernel for Multimedia devices– Video input (codec & camera) & Radio– However, as long as the kernel has..:

• Gstreamer/OpenMAX plugins• A method to share with other F/W via DMABUF of

UMM

• If V4L2/VB2 is used, things get easier.

V4L2 / VB2


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20Tizen Kernel MM –OpenGL / G3D-GPU


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• Most ARM SoC GPUs (MALI, SGX, …) use their own memory manager– E.g., Exynos4412/4210 Tizen Reference Kernel

has Mali w/ UMM.• Mali DDK modified to be compatible with UMM-

DMABUF.

• If GPU drivers use DRM, it would be great.– (and make them GPL)

OpenGL / G3D-GPU


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22Graphic and Display Usage Scenario


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27Tizen kernel Buffer Sharing


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• Requirement from Tizen platform and hardware– Different Memory Managers: GEM, VB2, GPU-

adhoc, …– Share buffers

• w/o memcpy• From and to users• Never expose directly to users (e.g., physical

address)

UMM DMABUF!

Tizen Kernel Buffer Sharing (cont)


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• Introduced by Jesse Barker, 2011• Includes– DMABUF (sharing buffer)

• Export– GEM/VB2/… object DMABUF

• Import– DMABUF GEM/VB2/… object

• Userspace sees DMABUF as a File Descriptor

– DMA mapping API for allocation– CMA (Contiguous Memory Allocator)– IOMMU (MMU for I/O devs)

Unified Memory Management (UMM)


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• Camera App1)Request V4L2 camera buffer (U)2)Allocate CMA buffer (K)3)Request a camera frame at the V4L2 buffer (U)4)Store the camera frame & Notify user (K)5)Request DMABUF export for the V4L2 camera buffer (U)6)dma_buf_exporter() (K)

• Create DMABUF from V4L2 buffer

7)dma_buf_fd() (K)• Provide FD of the DMABUF to user

DMA Buffer Sharing Example


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DMA Buffer Sharing Example (cont)


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• Camera App8)Request FD->GEM conversion (U) 9)dma_buf_get(fd) (K)

• Get DMABUF from FD

10)dma_buf_attach(dma-buf) / dma_buf_map_attachment() (K)

• Get Buffer from DMABUF

11)Import as GEM, send user (K) 12)Request GEM object name (U) 13)Return GEM object name (K) 14)Send GEM object name to X (U)



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• Camera App8)Request FD->GEM conversion (U) 9)dma_buf_get(fd) (K)

• Get DMABUF from FD

10)dma_buf_attach(dma-buf) / dma_buf_map_attachment() (K)

• Get Buffer from DMABUF

11)Import as GEM, send user (K) 12)Request GEM object name (U) 13)Return GEM object name (K) 14)Send GEM object name to X (U)



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• X server 15)Convert given GEM object name to GEM. Display its content. (U & K)



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• Close after usage1)“Free” the GEM object (U)2)Remove reference from the DMABUF (K)3)Close(DMABUF-FD) at cam app (U)4)(No more reference to DMABUF) Release callback executed (K)



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38Buffer Synchronization


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• Simple Usage Scenario– 1. CPU writes to buffer1.– 2. CPU tells GPU to do something on buffer1.– 3. GPU does something on buffer1.

• GPU finishes.

– 4. CPU reads the buffer1

Problem Definition

CPU GPU

BUS

DRAM

1 2

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How to ensure CPU won’t use buffer 1 until step 4?


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• What if there are two threads using GPU?– And if the two look at the same buffer?

• Not even aware of it?

• What if the two DMA devices (GPU, FIMC) share buffer?– But hard to know it at drivers or user threads.– FIMC never knows when GPU finishes– FIMC never knows when Threads1 stops using

“buffer1”– Threads2 never know when GPU stops using “buffer1”

Problem Definition (cont)


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• TGL (Tizen Global Lock) @ Tizen 2.0– … Let userspace handle the issue …– Kernel patch required.

• Sync Framework (Google)– Jun, 2012. Resources w/o DMABUF (similar with

TGL)

• KDS (Kernel Dependency System, ARM)– May 2012 / DMABUF-compatible

• DMA Fence Framework (Canonical/TI)– Aug 2012 / DMABUF-compatible– Work-In-Progress

Buffer Synchronization


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K-dbus


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• D-Bus– Message bus system– Method Call transaction– Signals– Broadcasting

Kdbus –D-bus is?


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• Low-level, native kernel D-Bus transport– All communication between processes take place

over special character device nodes in /dev/kdbus

• Receiver buffers– Single copy to destinations

• memfds– File descriptor for memory regions– Zero copy implementation

Kdbus –K-dbus is?


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Others


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• Yet Another Weird Ad-hoc Kernel Hacks Removed

• Manage status of cable & ports– A port with multiple cables (docks, multi-cables, …)– A port with multiple modes (USB, HDMI, TA, …)

• 3.5pi: stereo, stereo+mic, stereo+mic+buttons, stereo+buttons, mono, …

• Compatible with Switch– Android Switch drivers can be easily ported

• Refer to Linux/Documentation (porting guide for switch driver)

– Extcon drivers export both Switch and Extcon interfaces (compat mode)

• In Reference Device– MUIC (USB+HDMI+TA+DOCK+…)– 3.5Pi Jack

EXTCON (External Connector)


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• Charger Manager (/drivers/power/charger-manager.c)– All needed by Tizen user space are prepared– No OAL modification required

• OR supply battery/charger interface with power-supply-class

• Use EXTCON for Cable-Input (MUIC in mobile)– Switch class is no longer available in Linux.

• Note: some SOC (state-of-charge) value is required for mobile profile. Unless, Tizen will assume that SOC is 0 Shutdown!

Charger


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• Recommendation For Tizen3.0 or later– Do not use DVFS (CPUfreq/Devfreq) min/max

ABIs• PASS (Power-Aware System Service in Deviced) uses

– Use (keep their standard ABIs for PASS)• CPUfreq& Devfreq(DVFS for non CPU devices if you

have them)• Thermal FW

– PASS gives hints to DVFS/Hotplug• based on the info from user space.• based on the other kernel ABIs (e.g., Thermal)• highly configurable. (control knob of performance &

power)

Power Management

Embedded Software Lab. @ SKKU 49 1 Sungkyunkwan University Tizen Linux Kernel.

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Transcript of Embedded Software Lab. @ SKKU 49 1 Sungkyunkwan University Tizen Linux Kernel.