Re: [XEN][PATCH v10 12/20] xen/smmu: Add remove_device callback for smmu_iommu ops

[Michal Orzel]

On 30/08/2023 00:45, Stefano Stabellini wrote:
> 
> 
> On Tue, 29 Aug 2023, Michal Orzel wrote:
>> On 25/08/2023 10:02, Vikram Garhwal wrote:
>>> Add remove_device callback for removing the device entry from smmu-master 
>>> using
>>> following steps:
>>> 1. Find if SMMU master exists for the device node.
>>> 2. Check if device is currently in use.
>> Since you removed a call to iommu_dt_device_is_assigned_locked(), you do not 
>> check it from SMMU, right?
>> You are relying on a check done in iommu_remove_dt_device().
>> This wants to be mentioned. However, Julien suggested to do the check for 
>> internal SMMU state.
>> Looking at the code, when the device is assigned, we do:
>> dev_iommu_domain(dev) = domain;
>> and when de-assigned:
>> dev_iommu_domain(dev) = NULL;
>>
>> This means that before calling remove_smmu_master() you could do:
>>
>> /* Make sure device is not assigned */
>> if (dev_iommu_domain(dev))
>>     return -EBUSY;
>>
>> @Julien, @Stefano?
> 
> I think it is OK without it, as we have a call to
> iommu_dt_device_is_assigned_locked(np) already in
> iommu_remove_dt_device?

Yes, but this would add an extra layer of protection by checking for IOMMU 
domain for this device.

~Michal