On Friday, 27 July 2018 21:31:34 MSK Joerg Roedel wrote:

On Fri, Jul 27, 2018 at 11:13:31AM -0600, Rob Herring wrote:

quoted

I don't follow why we need a property rather than being implied by the
device's (the GPU) compatible string.

There might be devices where either setup works, with or without IOMMU
translation, and the firmware can set the property depending on whether
the user wants more performance or more security.

If we have a whitelist in the kernel this gets more complicated, we
probably need additional kernel-parameters to overwrite those whitelist
entries. Having a property in the device-tree seems to be a better way
here, imho.

IIUC, device-tree should be considered to be "written in stone" for a consumer 
device and hence firmware property isn't something that could be easily 
changed. The kernel-parameter will be much more universal. Anyway the global 
whitelisting should be a different topic for discussion, right now we need a 
kind of private whitelisting that is internal to kernel.



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