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Message-ID: <e23c8ffd6667e675ab80c83c39f8b91beb591328.camel@gmail.com>
Subject: Re: [PATCH v4 5/7] powerpc/iommu: Move iommu_table cleaning routine
 to iommu_table_clean
From:   Leonardo Bras <leobras.c@gmail.com>
To:     Brian King <brking@linux.vnet.ibm.com>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Joel Stanley <joel@jms.id.au>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        Ram Pai <linuxram@us.ibm.com>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Date:   Wed, 22 Jul 2020 20:45:25 -0300
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         <51235292-a571-8792-c693-d0dc6faeb21c@ozlabs.ru>
         <0f4c2d84d0958e98e7ada53c25750fe548cadf0b.camel@gmail.com>
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Organization: IBM
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On Tue, 2020-07-21 at 19:52 -0500, Brian King wrote:
> > 
> > As of today, there seems to be nothing like that happening in the
> > driver I am testing. 
> > I spoke to Brian King on slack, and he mentioned that at the point DDW
> > is created there should be no allocations in place.
> 
> I think there are a couple of scenarios here. One is where there is a DMA
> allocation prior to a call to set the DMA mask. Second scenario is if the
> driver makes multiple calls to set the DMA mask. I would argue that a properly
> written driver should tell the IOMMU subsystem what DMA mask it supports prior
> to allocating DMA memroy. Documentation/core-api/dma-api-howto.rst should
> describe what is legal and what is not.
> 
> It might be reasonable to declare its not allowed to allocate DMA memory
> and then later change the DMA mask and clearly call this out in the documentation
> if its not already.
> 
> -Brian

Thank you for the feedback Brian!

That makes sense to me. I will try to have this in mind for the next
patchset. 

Best regards,