From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [RFC v1 02/15] vt-d: VT-d Posted-Interrupts feature
 detection
Date: Fri, 27 Mar 2015 10:06:05 +0000
Message-ID: <55152B8D.3020102@citrix.com>
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To: "Wu, Feng" <feng.wu@intel.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Cc: "Zhang, Yang Z" <yang.z.zhang@intel.com>, "Tian,
	Kevin" <kevin.tian@intel.com>, "keir@xen.org" <keir@xen.org>, "JBeulich@suse.com" <JBeulich@suse.com>
List-Id: xen-devel@lists.xenproject.org

On 27/03/15 01:21, Wu, Feng wrote:
>>> +     * Remapping, and Posted Interrupt
>>>         */
>>>        for_each_drhd_unit ( drhd )
>>>        {
>>> @@ -2146,7 +2148,13 @@ int __init intel_vtd_setup(void)
>>>                iommu_qinval = 0;
>>>
>>>            if ( iommu_intremap && !ecap_intr_remap(iommu->ecap) )
>>> +        {
>>>                iommu_intremap = 0;
>>> +            iommu_intpost = 0;
>>> +        }
>>> +
>>> +        if ( iommu_intpost && !cap_intr_post(iommu->cap))
>> Missing space inside the outer bracket.
>>
>> I am wondering whether it might be easier, instead of having
>> "iommu_intremap = 0; iommu_intpost = 0" all over the place, to instead
>> insist that one must check "iommu_intremap && iommu_intpost".
> It that case, user must check "iommu_intremap && iommu_intpost" together,
> my idea in this patchset is the when iommu_intpost == 1 guarantees "iommu_intremap == 1",
> so we only need to check iommu_intpost later.

If the configuration gets much more complicated, it might be worth 
introducing iommu_disable(foo)/iommu_enable(foo) functions which take 
care of ensuring that the interdependences are met.

For now, this is probably the more simple solution.

>> Out of interest, which platforms have intpost capabilities?
> Another Broadwell platform, not launched yet.

Broadwell EP/EX ?  I have an SDP to hand, but as it claims to be a 
"Genuine Intel(R) CPU 0000 @ 1.70GHz", it is not completely trivial to 
work out what platform it is exactly.

~Andrew