Re: IOMMU problem on Xen dom0 arm (Was: Re: Xen on arm Chromebook seems to cause no display on screen)

[Chuck Zmudzinski <brchuckz@xxxxxxxxxxxx>]

On 10/27/2023 10:40 AM, Chuck Zmudzinski wrote:
> On 10/27/2023 9:44 AM, Julien Grall wrote:
>> Hi Chuck,
>> 
>> On 27/10/2023 04:42, Chuck Zmudzinski wrote:
>>> On 10/26/2023 5:24 PM, Julien Grall wrote:
>>>> I am not quite too sure why the check implies the IOMMU is not
>>>> supported. That said, I vaguely recall that Linux will update the DMA
>>>> ops when running under Xen. Would you be able to print the two values
>>>> returned ("%pS" should give the symbol)?
>>> 
>>> I got those values:
>>> 
>>> [    2.552094] [drm] dma_ops(priv->dma_dev): 0xc0d018c0, 
>>> dma_ops(subdrv_dev): 0xc0d662dc
>>> 
>>> I presume you know how to interpret those. The failed test is that they are 
>>> not equal.
>> 
>> Unfortunately the values are specific to the kernel build.
>> 
>>  From [1], I was expecting that %pS would print something like:
>> 
>>      %pS     versatile_init+0x0/0x110
>> 
>> Can you use 'nm', gdb or addr2line to find out the associated the symbols?
> 
> From addr2line and nm, I get this:
> 
> 0xc0d018c0 is in dma_mapping.c, symbol is iommu_ops

Sorry, that is dma-mapping.c

> 
> 0xc0d662dc is in swiotlb-xen.c, symbol is xen_swiotlb_dma_ops
> 
> Details:
> 
> user@linux:~/kernelbuild/linux-6.1.59$ addr2line -e vmlinux
> 0xc0d018c0
> dma-mapping.c:?
> 0xc0d662dc
> swiotlb-xen.c:?
> 
> user@linux:~/kernelbuild/linux-6.1.59$ nm vmlinux | grep c0d018c0
> c0d018c0 d $d
> c0d018c0 d iommu_ops
> user@linux:~/kernelbuild/linux-6.1.59$ nm vmlinux | grep c0d662dc
> c0d662dc d $d
> c0d662dc D xen_swiotlb_dma_ops
> user@linux:~/kernelbuild/linux-6.1.59
> 
>> 
>> Cheers,
>> 
>> [1] https://www.kernel.org/doc/Documentation/printk-formats.txt
>> 
>