[PATCH] drm/tegra: Stop using iommu_present()

[Robin Murphy]

On 2022-04-06 15:32, Dmitry Osipenko wrote:
> On 4/5/22 17:19, Robin Murphy wrote:
>> Remove the pointless check. host1x_drm_wants_iommu() cannot return true
>> unless an IOMMU exists for the host1x platform device, which at the moment
>> means the iommu_present() test could never fail.
>>
>> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
>> ---
>>   drivers/gpu/drm/tegra/drm.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
>> index 9464f522e257..bc4321561400 100644
>> --- a/drivers/gpu/drm/tegra/drm.c
>> +++ b/drivers/gpu/drm/tegra/drm.c
>> @@ -1149,7 +1149,7 @@ static int host1x_drm_probe(struct host1x_device *dev)
>>   		goto put;
>>   	}
>>   
>> -	if (host1x_drm_wants_iommu(dev) && iommu_present(&platform_bus_type)) {
>> +	if (host1x_drm_wants_iommu(dev)) {
>>   		tegra->domain = iommu_domain_alloc(&platform_bus_type);
>>   		if (!tegra->domain) {
>>   			err = -ENOMEM;
> 
> host1x_drm_wants_iommu() returns true if there is no IOMMU for the
> host1x platform device of Tegra20/30 SoCs.

Ah, apparently this is another example of what happens when I write 
patches late on a Friday night...

So on second look, what we want to ascertain here is whether dev has an 
IOMMU, but only if the host1x parent is not addressing-limited, either 
because it can also use the IOMMU, or because all possible addresses are 
small enough anyway, right? Are we specifically looking for the host1x 
having a DMA-API-managed domain, or can that also end up using the 
tegra->domain or another unmanaged domain too? I can't quite figure out 
from the comments whether it's physical addresses, IOVAs, or both that 
we're concerned with here.

Thanks,
Robin.