AM335x GPMC using DMA

Alex Shneur

Hi, I have a user-space application that reads/writes data to an external memory using GPMC. Also I have a kernel-space application (module) that transfers data from memory to memory. How should I send the addresses of source and destination buffers into the module in order to make a dma-transaction in it? In user-space I use mmap-function to operate with the GPMC (I asked about it in this topic: https://e2e.ti.com/support/arm/sitara_arm/f/791/t/447099 ) and in kernel-space I use EdmaTest application from here: processors.wiki.ti.com/.../EDMA_sample_test_application. I can send an integer or string variable to the module, but I can't understand how to send a correct address because, in my opinion, there are different address spaces in user and kernel spaces. Maybe there is another way to send data through GPMC using DMA on am335x-processor, I don't know. Please, get me some useful advice how to solve this problem (I'm using Linux kernel 3.12 from TI SDK).

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

I will forward this to the SW team.

0 Alex Shneur over 9 years ago in reply to Biser Gatchev-XID

Prodigy 210 points

Biser, why do you think that my question is related to SW? As I've said, I was using Linux kernel 3.12 from TI SDK, but not Starterware. Please, leave this question here.

0 Biser Gatchev-XID over 9 years ago in reply to Alex Shneur

TI__Guru**** 393215 points

SW = software, sorry if you misunderstood me.

0 Alex Shneur over 9 years ago in reply to Biser Gatchev-XID

Prodigy 210 points

Sorry, I haven't really understood you. Thank you for your explanation.

0 Yordan Kovachev over 9 years ago

TI__Guru**** 161600 points

Hi,
In user space you pass the apis the physical address of a memory location/hw register. The api is responsible to remap this address and pass the virtualized address to the kernel.
As a reference I usually take the devmem2 utility:

#define MAP_SIZE 4096UL

#define MAP_MASK (MAP_SIZE - 1)
void *map_base, *virt_addr;
/*then the virtualization of the physical address is performed as shown bellow; target = physical address*/
map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);
virt_addr = map_base + (target & MAP_MASK);

You need to do similar remapping in your kernel module, in order to process the physical address of the memory location passed to it by a user space api.

Best Regards,
Yordan

0 Alex Shneur over 9 years ago in reply to Yordan Kovachev

Prodigy 210 points

Hi Yordan,
I've tried to use open and mmap functions in the kernel space, but I'd got errors while compiling a module using make function. Here is my code:
int fd = open("/dev/mem", O_RDWR|O_SYNC);
__mmapl = (uint32_t*) mmap(NULL, 0x20000000, PROT_READ|PROT_WRITE, MAP_SHARED, fd, MMAP_OFFSET);

And errors:
error: implicit declaration of function ‘open’ [-Werror=implicit-function-declaration]
implicit declaration of function ‘mmap’ [-Werror=implicit-function-declaration]

0 Yordan Kovachev over 9 years ago in reply to Alex Shneur

TI__Guru**** 161600 points

Hi,

Address remapping in kernel sources is done using the ioremap() function. And then use __raw_readl()/__raw_writel() functions on the same address. For example if you want to read what is set in address 0x50000000 (GPMC REV register) you need to use:

static void __iomem *gpmc_rev_base;
gpmc_rev_base = ioremap(0x50000000, 32);
unsigned long int temp = __raw_readl(gpmc_rev_base);
printk("\n========GPMC REV is %x================\n", temp);

Same thing is valid for CS memory region. But have in mind that in order to access the CS address region you must correctly initialize the GPMC CS first.

Best Regards,
Yordan

0 Alex Shneur over 9 years ago in reply to Yordan Kovachev

Prodigy 210 points

Yordan, thank you for your help, this code works fine.

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AM335x GPMC using DMA