Introduction
This document intends to describe how to implement workaround for ERR050145 (ISI: Memory overwrite occurring outside of allocated buffer space corrupting system memory) based on Linux BSP. ERR050145 is applicable for i.MX8QM B0, i.MX8QXP B0 series products.
Software Platform
Reference patches stated into this document are developed and validated on L4.14.98_GA2.0.0 release.
Software Workaround
As workaround stated, the xRDC can be programmed to grant write access to the ISI only within its allocated frame buffer space, which can prevent the corruption. So under Linux, we can consider to implement workaround like so: Create children partition for ISI and allocate buffers. Then Linux can access these buffers as normal, but ISI can't access other memory out of these buffers, it is limited by xRDC hardware.
Considering the xRDC hardware can only support up to 16 memory regions, we may need to consider different workaround implementations for different camera use case scenarios.
For single camera use case, the required camera buffer number is usually less than 16. So “0001-iMX8QM-iMX8QX-ERR050145-ISI-overwrite-workaround.patch” is enough. No modification is needed for camera application in this case.
For multiple camera use case, all patches (0001~0003) are needed. If the camera application used VB2_MEMORY_MMAP memory mode, then no code modification is needed in application. The V4l2 ISI driver can handle everything (Allocate physical continued memory for each camera, and map them as one xRDC memory region for overwrite protect). If the camera application used VB2_MEMORY_USERPTR and VB2_MEMORY_DMABUF memory mode, then it needs allocate camera buffers with physical continued memory for each camera, then the driver will merge them as one xRDC memory region in SCFW.
How to prove workaround take effective?
After applying the patches, the ISI will report AXI_WR_ERR due to it failed to write data out of the allocated buffers when the errata happens.
To reduce the ISI interrupt, we can also change the ISI interrupt setting as followed:
void mxc_isi_enable_irq(struct mxc_isi_dev *mxc_isi)
{
u32 val;
val = CHNL_IER_FRM_RCVD_EN_MASK |
CHNL_IER_EXCS_OFLW_V_BUF_EN_MASK |
CHNL_IER_EXCS_OFLW_U_BUF_EN_MASK |
CHNL_IER_EXCS_OFLW_Y_BUF_EN_MASK;
writel(val, mxc_isi->regs + CHNL_IER);
}
Add reference patch for L5.4.70_2.3.0 and L5.10.72_2.2.0.
