[Qemu-devel] SPARC iommu mapping

[Joerg Platte <lists@naasa.net>]

Hi!

I still have problems when using a disk image for the SPARC system emulator. 
Reading and writing now works better than in previous versions, but sometimes 
data written to image is simply corrupt. To find this problem I wrote a small 
program writing data to the beginning of a disk image. Afterwards I compared 
the written data in the image with the expected values. Most of the data was 
correct, but sometimes a few pages mostly contains only zeros. 

To find this problem, I enabled debugging in the esp.c file and printed the 
mapped address (after iommu mapping). In some cases the mapped address is 
zero:

Normal write:

ESP: DMA Direction: r, addr 0x008fd000 0000000b
ESP: DMA Direction: r, addr 0x0bea1000 0000e000
ESP: DMA address 0bea2000
ESP: DMA address 0bea4000
ESP: DMA address 0bea5000
ESP: DMA address 0bea6000
ESP: DMA address 0bea7000
ESP: DMA address 0bea8000
ESP: DMA address 0bea9000
ESP: DMA address 0beaa000
ESP: DMA address 0beab000
ESP: DMA address 0beac000
ESP: DMA address 0bead000
ESP: DMA address 0beaf000
ESP: DMA address 0beb0000

Faulty write:

ESP: DMA Direction: r
ESP: DMA Direction: r, addr 0x008fd000 0000000b
ESP: DMA Direction: r, addr 0x0beb1000 0000e000
ESP: DMA address 0beb2000
ESP: DMA address 0beb3000
ESP: DMA address 0beb4000
ESP: DMA address 0beb5000
ESP: DMA address 0beb6000
ESP: DMA address 0beb7000
ESP: DMA address 0beb8000
ESP: DMA address 00000000

I used this code in handle_ti to produce this output:

	    dmaptr = iommu_translate(s->espdmaregs[1] + i);
	    if ((olddma&0xfffff000) != (dmaptr&0xfffff000)) {
		    DPRINTF("DMA address %08x\n", dmaptr);
		    olddma=dmaptr;
	    }


Unfortunately, I'm no hardware or SPARC expert and it took a whole day to 
track down this problem. So I'm not able to find the reason for this 
behaviour. What may cause the wrong mapping? Is this some kind of page fault, 
which must be handled by the kernel? Or just a bug?

regards,
Jörg