DMA Access

[Everaldo-Gomes]

Hi,
I'm trying to configure the DMA using this code, whose the addresses I found in the raspberry pi 4b documentation.

#define DMA_BASE       0xFE007000
#define DMA_CHANNEL_0  (DMA_BASE + 0x000)

typedef struct
{
    uint32_t TI;
    uint32_t SOURCE_AD;
    uint32_t DEST_AD;
    uint32_t TXFR_LEN;
    uint32_t STRIDE;
    uint32_t NEXTCONBK;
    uint32_t RESERVED[2];
} DMA_ctrl_block;

core/init.c:
if (cpu()->id == CPU_MASTER)
{
    volatile uint32_t *DMA_CS = (uint32_t *)(DMA_CHANNEL_0);
    printk("%p %x\n", DMA_CS, *DMA_CS); 
}	

Right after trying to access any register, Bao reports the following error.

Starting application at 0x00100000 ...
x0: 0x00000000fe007000
x1: 0x0000000000000000
x2: 0x0000fd800001cc10
x3: 0x0000000000000000
x4: 0x0000fd8000046000
x5: 0x00000000fe215000
x6: 0x0000fd8000046000
x7: 0x000000000000000d
x8: 0x0000000000000000
x9: 0x0000000000000000
x10: 0x000000000000000f
x11: 0x0000000000000001
x12: 0x0000fd8000016ef0
x13: 0x0000000000000018
x14: 0x0000000000000018
x15: 0x0000000000000001
x16: 0x0000fd8000021078
x17: 0x0000fd8000021078
x18: 0x00000000000c7000
x19: 0x0000000000000000
x20: 0x00000000000000a8
x21: 0x0000000000000002
x22: 0x0000000007b42c00
x23: 0x0000000000000002
x24: 0x0000000007fc4944
x25: 0x0000000000000000
x26: 0x0000000000000000
x27: 0x0000000000000000
x28: 0x0000000007b42c60
x29: 0x0000fe0000001fd0
x30: 0x0000fd800000c2d4
SP: 0x0000fe0000001fd0
ESR: 0x0000000096000004
ELR: 0x0000fd800000c300
FAR: 0x00000000fe007000
BAO ERROR: cpu0 internal hypervisor abort - PANIC

I'd like to know how addresses are organized or mapped in Bao and how can I use DMA, to map specific memory regions/banks for each CPU to use. Is DMA the right component to do this?

Platform: Raspberry Pi 4b
Demo: Dual-guest Linux+FreeRTOS

[josecm]

@Everaldo-Gomes sorry! This one slipped through the cracks! Please sends us a direct email if we fail to respond in a few days!

TBH, I don't know if I fully get your question. Are you trying to use the DMA directly within Bao? If so, you need to map that device's MMIO region in Bao's address space! Take a look at how, for example, Bao maps the GIC during initialization in gic_map_mmio using the mem_alloc_map_dev function to understand which API and arguments to use for that.

An important point is also that, raspberry PI does not have an SMMU/IOMMU. Also, Bao is not equipped to add its context to an SMMU even if there was any. To solve this, after you successfully are able to access the DMA within Bao, you need to translate any addresses you pass to it using the mem_translate function.

Let me know if this helps you

[Everaldo-Gomes]

Hi,
trying to follow the steps from your response, I did the following:

void dma_map_mmio(void)
{
    struct addr_space* as = &cpu()->as;
    size_t num_pages = DMA_SIZE / DMA_PAGE_SIZE;

    dma_vaddr = mem_alloc_map_dev(as, <some_sec>, INVALID_VA, DMA_BASE, num_pages);
    
    if (dma_vaddr == INVALID_VA)
       printk("ERROR!!!\n");

    printk("DMA MMIO mapped at virtual address: %p\n", (void*)dma_vaddr);
}

void test_dma_access(void)
{
    if (dma_vaddr == INVALID_VA)
    {
        printk("DMA MMIO not mapped!\n");
        return;
    }

    volatile uint32_t *DMA_CS = (uint32_t *)(dma_vaddr);
    printk("DMA Control Status register at %p: 0x%x\n", DMA_CS, *DMA_CS);
}

In the dma_map_mmio, I tested the variable <some_sec> with the values in the AS_SEC enum.

 SEC_HYP_GLOBAL = 0 -> 0x4a000
 SEC_HYP_IMAGE,     -> 0x4a000
 SEC_HYP_PRIVATE,   -> 0x3000
 SEC_HYP_VM,        -> 0x0
 SEC_HYP_ANY,       -> error
 SEC_VM_ANY = 0,    -> 0x4a000

For any of these values the printk("DMA MMIO mapped at the virtual address: %p\n", (void*)dma_vaddr); in dma_map_mmio is always empty.

The value (*DMA_CS) showed in printk("DMA Control Status Register at %p: 0x%x\n", DMA_CS, *DMA_CS); in test_dma_access is also empty, but the addresses (DMA_CS) in this same printk depends of the AS_SEC is used, which are the values on the right side of the AS_SEC enum.

The GIC uses SEC_HYP_GLOBAL but I'm not sure if I have to use it as well, I don't know if the process to map was correct, and also not sure where is the right place to use mem_translate is before or after the calling mem_alloc_map_dev?