As per the plat-omap/dma.c the function is like this:
/* * Returns current physical source address for the given DMA channel. * If the channel is running the caller must disable interrupts prior calling * this function and process the returned value before re-enabling interrupt to * prevent races with the interrupt handler. Note that in continuous mode there * is a chance for CSSA_L register overflow inbetween the two reads resulting * in incorrect return value. */ dma_addr_t omap_get_dma_src_pos(int lch) { dma_addr_t offset;
if (cpu_class_is_omap1()) offset = (dma_addr_t) (OMAP1_DMA_CSSA_L_REG(lch) | (OMAP1_DMA_CSSA_U_REG(lch) << 16));
if (cpu_is_omap24xx()) offset = OMAP_DMA_CSAC_REG(lch);
return offset; }
I have one doubt here, I am referring Writing ALSA driver by Takashi it says following about the dma_addr_t.
If you use a standard ALSA function, snd_pcm_lib_malloc_pages(), for allocating the buffer, these fields are set by the ALSA middle layer, and you should not change them by yourself.
I am using the standard helper function to allocate the DMA buffer in my hw_params, so I am not setting the runtime->dma_addr field, pcm layer must be setting it, right?
But in my pointer function I am accessing runtime->dma_addr where as the guide says it is i.e the physical bus address is not accessible from the main CPU. I am doing wrong accessing it?
After allocating the buffer in hw_params i am trying to check the physical and virtual addr of the DMA buffer, I get
Physical DMA addr is 00000000 and virtual addr is c3540000
does it mean that dma_addr is really not accessible from main CPU?
In pointer when I check the dma addr I get
runtime->dma_addr is 00000000 !!
How come??
-pharaoh.
On 6/26/07, Clemens Ladisch cladisch@fastmail.net wrote:
Pharaoh . wrote:
src = omap_get_dma_src_pos(s->lch[s->dma_q_head]); offset = src - runtime->dma_addr; printk("src is %u and offset is %u\n",dest,offset);src is 3246792928 and offset is 3304194048 Returning pos = 20742144 ALSA sound/core/pcm_lib.c:167: BUG: stream = 0, pos = 0x13c8000, buffer
size = 0x4000, period size = 0x800
dma_addr = 0xFC9420E0 (is this correct?) src = 0xC18620E0 offset = 0xC4F20000
Apparently, the return value of omap_get_dma_src_pos() is wrong. Should this value be 16 bits?
Regards, Clemens