DMA driver. Cache.

[virgil]

Hi all,

I'm having troubles with the following piece of code. It's a DMA
driver written in kernel, for MPC8245. Local to local memory.
The issue is: the values I see at the end of the transfer are the
uninitilized source values, instead of the initialized ones. It looks
like a cache problem. If it is I don't know how to invalidate the data
cache. Or, is it the type of memory I'm using?

Thanks,
Virgil

static int direct_dma_init(void)
{
U8* scr;
U32 tt;
int i;
sursa = kmalloc(64,GFP_KERNEL|GFP_DMA);
//sursa = __get_dma_pages(GFP_KERNEL,0);
dest = kmalloc(64,GFP_KERNEL|GFP_DMA);

printk("sursa:%x %x %x %x %x
%x\n",sursa[0],sursa[1],sursa[2],sursa[3],sursa,dest); // these are
the values I see at the end of dma transfer
dma_t = (volatile DMAS*) ioremap(DMA_SPACE(0),sizeof(DMAS));
dma_r = (volatile DMAS*) ioremap(DMA_SPACE(1),sizeof(DMAS));
for(i=0;i<8;i++)
{
sursa[i] = i+40;
}

printk("sursa:%x %x %x
%x\n",sursa[0],sursa[1],sursa[2],sursa[3]);//these should be the
values I see
printk("dma:%x %x %x %x\n",dma_t,dma_r,DMA_SPACE(0),DMA_SPACE(1));


if (readl(&dma_t->dsr) & 0x4) {
printk("nu pe aici0");
return;
}
writel(virt_to_bus(sursa),&dma_t->sar);//source address
writel(virt_to_bus(dest),&dma_t->dar);//destination address
writel(4,&dma_t->bcr);// 4 bytes to transfer
writel(0,&dma_t->cdar);
printk("prim %x %x %x %x %x %x\n",
(((U32)readl(&dma_t->dmr))),(((U32)readl(&dma_t->dsr))),
(((U32)readl(&dma_t->cdar))),(((U32)readl(&dma_t->sar))),
(((U32)readl(&dma_t->dar))),(((U32)readl(&dma_t->bcr))));

writel(4,&dma_t->dmr);
writel(5, &dma_t->dmr);// start dma

tt = readl(&dma_t->dsr);
writel(tt,&dma_t->dsr);
while(tt&0x4){ // just in case: wait to finish
tt = readl(&dma_t->dsr);
writel(tt,&dma_t->dsr);
}
printk("prim %x %x %x %x %x %x \n",
(((U32)readl(&dma_t->dmr))),(((U32)readl(&dma_t->dsr))),
(((U32)readl(&dma_t->cdar))),(((U32)readl(&dma_t->sar))),
(((U32)readl(&dma_t->dar))),(((U32)readl(&dma_t->bcr))));

printk("\ndest:%x %x %x %x",dest[0],dest[1],
dest[2],dest[3]);

}

[John Williams]

Post by virgil
I'm having troubles with the following piece of code. It's a DMA
driver written in kernel, for MPC8245. Local to local memory.
The issue is: the values I see at the end of the transfer are the
uninitilized source values, instead of the initialized ones. It looks
like a cache problem. If it is I don't know how to invalidate the data
cache. Or, is it the type of memory I'm using?

most (all?) platforms define a bunch of cache clearing functions in
include/asm/pgalloc.h or pgtable.h

cd linux-2.4.x/include/asm-xxxxx

grep flush *.h

Rgds,

John