linux-kernel - Re: [PATCH 4/4] powerpc/pseries/iommu: Remove default DMA window before creating DDW

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Date:   Tue, 23 Jun 2020 13:52:06 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Leonardo Bras <leobras.c@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] powerpc/pseries/iommu: Remove default DMA window
 before creating DDW



On 23/06/2020 12:43, Leonardo Bras wrote:
> On Tue, 2020-06-23 at 12:35 +1000, Alexey Kardashevskiy wrote:
>>> I am not sure if this is true in general, but in this device (SR-IOV
>>> VF) I am testing it will return 0 windows if the default DMA window is
>>> not deleted, and 1 after it's deleted.
>>
>> Since pHyp can only create windows in "64bit space", now (I did not know
>> until a few month back) I expect that thing to return "1" always no
>> matter what happened to the default window. And removing the default
>> window will only affect the maximum number of TCEs but not the number of
>> possible windows.
> 
> Humm, something gone wrong then.
> 
> This patchset was developed mostly because on testing, DDW would never
> be created because windows_available would always be 0.

? On phyp, if there is a huge window, then it can be 0 or 1. On KVM, it
is 0 or 1 or 2.


> 
> I will take a deeper look in that.
> 
> Best regards,
> Leonardo
> 

-- 
Alexey