Adding Roger and Jan to the conversation.
Please see below.
On 23/06/2025 00:30, Stefano Stabellini wrote:
> On Thu, 19 Jun 2025, Oleksii Moisieiev wrote:
>> On 18/06/2025 03:04, Stefano Stabellini wrote:
>>> On Thu, 12 Jun 2025, Oleksii Moisieiev wrote:
>>>> Hi Stefano,
>>>>
>>>> I'm very sorry for a long silence. Please see my answers below:
>>>>
>>>> On 22/05/2025 03:25, Stefano Stabellini wrote:
>>>>> On Mon, 19 May 2025, Oleksii Moisieiev wrote:
>>>>>> From: Grygorii Strashko<grygorii_stras...@epam.com>
>>>>>>
>>>>>> Add chained handling of assigned DT devices to support access-controller
>>>>>> functionality through SCI framework, so DT device assign request can be
>>>>>> passed to FW for processing and enabling VM access to requested device
>>>>>> (for example, device power management through FW interface like SCMI).
>>>>>>
>>>>>> The SCI access-controller DT device processing is chained after IOMMU
>>>>>> processing and expected to be executed for any DT device regardless of
>>>>>> its
>>>>>> protection by IOMMU (or if IOMMU is disabled).
>>>>>>
>>>>>> This allows to pass not only IOMMU protected DT device through
>>>>>> xl.cfg:"dtdev" property for processing:
>>>>>>
>>>>>> dtdev = [
>>>>>> "/soc/video@e6ef0000", <- IOMMU protected device
>>>>>> "/soc/i2c@e6508000", <- not IOMMU protected device
>>>>>> ]
>>>>>>
>>>>>> The change is done in two parts:
>>>>>> 1) update iommu_do_dt_domctl() to check for dt_device_is_protected() and
>>>>>> not fail if DT device is not protected by IOMMU
>>>>>> 2) add chained call to sci_do_domctl() in do_domctl()
>>>>>>
>>>>>> Signed-off-by: Grygorii Strashko<grygorii_stras...@epam.com>
>>>>>> Signed-off-by: Oleksii Moisieiev<oleksii_moisie...@epam.com>
>>>>>> ---
>>>>>>
>>>>>>
>>>>>>
>>>>>> xen/arch/arm/firmware/sci.c | 37
>>>>>> +++++++++++++++++++++++++
>>>>>> xen/arch/arm/include/asm/firmware/sci.h | 14 ++++++++++
>>>>>> xen/common/domctl.c | 19 +++++++++++++
>>>>>> xen/drivers/passthrough/device_tree.c | 6 ++++
>>>>>> 4 files changed, 76 insertions(+)
>>>>>>
>>>>>> diff --git a/xen/arch/arm/firmware/sci.c b/xen/arch/arm/firmware/sci.c
>>>>>> index e1522e10e2..8efd541c4f 100644
>>>>>> --- a/xen/arch/arm/firmware/sci.c
>>>>>> +++ b/xen/arch/arm/firmware/sci.c
>>>>>> @@ -126,6 +126,43 @@ int sci_assign_dt_device(struct domain *d, struct
>>>>>> dt_device_node *dev)
>>>>>> return 0;
>>>>>> }
>>>>>>
>>>>>> +int sci_do_domctl(struct xen_domctl *domctl, struct domain *d,
>>>>>> + XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
>>>>>> +{
>>>>>> + struct dt_device_node *dev;
>>>>>> + int ret = 0;
>>>>>> +
>>>>>> + switch ( domctl->cmd )
>>>>>> + {
>>>>>> + case XEN_DOMCTL_assign_device:
>>>>>> + ret = -EOPNOTSUPP;
>>>>> Are you sure -EOPNOTSUPP is the right error code for the 3 checks below?
>>>> The -EOPNOTSUPP code is used because this is part of a chained call after
>>>> iommu_do_domctl, as stated in xen/common/domctl.c:859. The
>>>> XEN_DOMCTL_assign_device
>>>> call is expected to handle any DT device, regardless of whether the DT
>>>> device is
>>>> protected by an IOMMU or if the IOMMU is disabled.
>>>> The following cases are considered:
>>>>
>>>> 1. IOMMU Protected Device (Success)
>>>>
>>>> If the device is protected by the IOMMU and iommu_do_domctl returns 0,
>>>> we continue
>>>> processing the DT device by calling sci_do_domctl.
>>>>
>>>> 2. IOMMU Disabled (-EOPNOTSUPP from iommu_do_domctl)
>>>>
>>>> If iommu_do_domctl returns -EOPNOTSUPP, indicating that the IOMMU is
>>>> disabled,
>>>> we still proceed to call sci_do_domctl.
>>> OK this makes sense. I think it is OK to have a special error code to
>>> say "the IOMMU is disabled" but I don't know if it is a good idea to try
>>> to use -EOPNOTSUPP for that. -EOPNOTSUPP could mean a hypervisor
>>> configuration with domctl disabled, for instance.
>>>
>>> It might be wiser to use a different error code. Maybe ENOENT?
>>>
>> I see that in the following commit:
>>
>> 71e617a6b8 (use is_iommu_enabled() where appropriate..., 2019-09-17)
>>
>> -ENOSYS return code was changed to -EOPNOTSUPP in iommu_do_domctl.
>>
>> It's not clear to me why this was done from the commit description.
>>
>> Maybe we should add commit author?
> Roger and Jan might know
