Re: drm/radeon: "ring test failed" on PA-RISC Linux

[Alex Ivanov <gnidorah@p0n4ik.tk>]

Let's go futher.

25.09.2013, 22:58, "Alex Ivanov" <gnidorah@p0n4ik.tk>:

>  25.09.2013, 21:28, "Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>:
>>   I took a look at the arch/parisc/kernel/pci-dma.c and I see that
>>   is mostly a flat platform. That is bus addresses == physical addresses.
>>   Unless it is an pclx or pclx2 CPU type (huh?) - if its it that
>>   then any calls to dma_alloc_coherent will map memory out of a pool.
>>   In essence it will look like a SWIOTLB bounce buffer.
>  arch/parisc/kernel/pci-dma.c:
>  ** PARISC 1.1 Dynamic DMA mapping support.
>  ** This implementation is for PA-RISC platforms that do not support
>  ** I/O TLBs (aka DMA address translation hardware).
>
>  That's very old. PA-RISC 2.0 came into the game circa 1996.
>  PA-RISC 1.1 is 32-bit only and i even not sure whether these machines
>  had PCI bus.
>
>  Only old boxes (PA7200 CPU and lower) cannot use dma_alloc_coherent()
>  (and forced to do syncs iirc). That's not our case.
>  And PA-RISC configs have 'Discontiguous Memory' choosen.
>>   But interestingly enough there is a lot of 'flush_kernel_dcache_range'
>>   call for every DMA operation.
>>  And I think the you need to do
>>   dma_sync_for_cpu call in the radeon_test_writeback for it to
>>   use the flush_kernel_dcache_range.

I was correct regarding syncs.
In our case (SBA IOMMU) dma_sync* calls are no-ops:

sba_iommu.c:
static struct hppa_dma_ops sba_ops = {
...
     .dma_sync_single_for_cpu =      NULL,
        .dma_sync_single_for_device =   NULL,
         .dma_sync_sg_for_cpu =          NULL,
        .dma_sync_sg_for_device =       NULL,
}

dma-mapping.h:
 dma_cache_sync(struct device *dev, void *vaddr, size_t size,
               enum dma_data_direction direction)
 {
        if(hppa_dma_ops->dma_sync_single_for_cpu)
                flush_kernel_dcache_range((unsigned long)vaddr, size);
 }

So i'll skip doing the flush_kernel_dcache_range().

>>  I don't know what the
>>   flush_kernel_dcache_range does thought so I could be wrong.
>  D-cache is a CPU cache (if they meant it).
>  Seems to be L1-level. There is an I-cache at same level.
>>   You are missing a translation here (you were comparing the virtual address
>>   to the bus address). I was thinking something along this:
>  Yes, this confused me. I've translated your suggestion literally :\
>>                   unsigned int pfn = page_to_pfn(ttm->pages[i]);
>>                   dma_addr_t bus =  gtt->ttm.dma_address[i];
>>                   void *va_bus, *va, *va_pfn;
>>
>>                   if ((pfn << PAGE_SHIFT) != bus)
>>                           printk("Bus 0x%lx != PFN 0x%lx, bus, pfn << PAGE_SHIFT); /* OK, that means
>>                           bus addresses are different */
>>
>>                   va_bus = bus_to_virt(gtt->ttm.dma_address[i]);
>>                   va_pfn = __va(pfn << PAGE_SHIFT);
>>
>>                   if (!virt_addr_valid(va_bus))
>>                           printk("va_bus (0x%lx) not good!\n", va_bus);
>>                   if (!virt_addr_valid(va_pfn))
>>                           printk("va_pfn (0x%lx) not good!\n", va_pfn);
>>
>>                   /* We got VA for both bus -> va, and pfn -> va. Should be the
>>                      same if bus and physical addresses are on the same namespace. */
>>                   if (va_bus != va_pfn)
>>                           printk("va bus:%lx != va pfn: %lx\n", va_bus, va_pfn);
>>
>>                   /* Now that we have bus -> pa -> va (va_bus) try to go va_bus -> bus address.
>>                      The bus address should be the same */
>>                   if (gtt->tmm.dma_address[i] != virt_to_bus(va_bus))
>>                           printk("bus->pa->va:%lx != bus->pa->va->ba: %lx\n", gtt->tmm.dma_address[i],virt_to_bus(va_bus));

Ok, slightly modified:

	struct page *page = ttm->pages[i];
	unsigned long pfn = page_to_pfn(page);
	dma_addr_t bus = gtt->ttm.dma_address[i];
	void *va_bus, *va, *va_pfn;

	BUG_ON(!pfn_valid(pfn));
	//BUG_ON(!page_mapping(page)); // Leads to a kernel BUG

/* Avoid floodage */
if (i % 100 == 0) {
	if ((pfn << PAGE_SHIFT) != bus)
		printk("Bus 0x%lx != PFN 0x%lx\n", bus, pfn << PAGE_SHIFT); /*
		OK, that means bus addresses are different */

	va_bus = bus_to_virt(bus);
	va_pfn = __va(pfn << PAGE_SHIFT);

	if (!virt_addr_valid(va_bus))
      		 printk("va_bus (0x%lx) not good!\n", va_bus);

	if (!virt_addr_valid(va_pfn))
		printk("va_pfn (0x%lx) not good!\n", va_pfn);

	/* We got VA for both bus -> va, and pfn -> va. Should be the
	same if bus and physical addresses are on the same namespace. */
	if (va_bus != va_pfn)
		printk("va bus: %lx != va pfn: %lx\n", va_bus, va_pfn);

	/* Now that we have bus -> pa -> va (va_bus) try to go va_bus -> bus address.
	The bus address should be the same */
	if (bus != virt_to_bus(va_bus))
		printk("bus->pa->va: %lx != bus->pa->va->ba: %lx\n", bus,virt_to_bus(va_bus));
}

Output:
Bus 0x40280000 != PFN 0x3e92d000
va_bus (0x80280000) not good!
va bus: 80280000 != va pfn: 7e92d000
Bus 0x40281000 != PFN 0x3e930000
va_bus (0x80281000) not good!
va bus: 80281000 != va pfn: 7e930000
...

va_bus is invalid. That's the reason i was getting a KF trying to read data behind it.

>>>                         DRM_INFO("MISMATCH: %p != %p\n", va, (void *) virt_to_bus(va));
>>>                         /*DRM_INFO("CONTENTS: %x\n", *((uint32_t *)va));*/ // Leads to a Kernel Fault
>>   That is odd. I would have thought it would be usuable.
>>>                         ...
>>>                    }
>>>
>>>    I'm getting the output:
>>>
>>>    [drm] MISMATCH: 0000000080280000 != 0000000040280000
>>   In theory that means the bus address that is programmed in (gtt->dma_address[i])
>>   is 0000000040280000 (which is what virt_to_bus(va) should have resolved itself to).
>  Should resolved properly. I had a sane check of virt_to_bus(va) == gtt->ttm.dma_address[i]
>>   Tha you can't get access to 'va' (0000000080280000) is odd. One way to try to
>>   access it is to do:
>>
>>           va = __va(page_to_pfn(ttm->pages[i]) << PAGE_SHIFT);
>>           DRM_INFO("CONTENTS: %x\n", *((uint32_t)va));
>>
>>   As that would get it via the page -> va.

This way i get CONTENTS: 0

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