linux-kernel - Re: [PATCH v5 01/14] drivers: iommu: add FWNODE

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Message-ID: <3178073.UTpgCTN6if@vostro.rjw.lan>
Date:   Thu, 29 Sep 2016 22:59:40 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Robin Murphy <robin.murphy@....com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Jon Masters <jcm@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Sinan Kaya <okaya@...eaurora.org>,
        Nate Watterson <nwatters@...eaurora.org>,
        Prem Mallappa <prem.mallappa@...adcom.com>,
        Dennis Chen <dennis.chen@....com>, linux-acpi@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 01/14] drivers: iommu: add FWNODE_IOMMU fwnode type

On Thursday, September 29, 2016 03:15:20 PM Lorenzo Pieralisi wrote:
> Hi Rafael,
> 
> On Fri, Sep 09, 2016 at 03:23:30PM +0100, Lorenzo Pieralisi wrote:
> > On systems booting with a device tree, every struct device is
> > associated with a struct device_node, that represents its DT
> > representation. The device node can be used in generic kernel
> > contexts (eg IRQ translation, IOMMU streamid mapping), to
> > retrieve the properties associated with the device and carry
> > out kernel operation accordingly. Owing to the 1:1 relationship
> > between the device and its device_node, the device_node can also
> > be used as a look-up token for the device (eg looking up a device
> > through its device_node), to retrieve the device in kernel paths
> > where the device_node is available.
> > 
> > On systems booting with ACPI, the same abstraction provided by
> > the device_node is required to provide look-up functionality.
> > 
> > Therefore, mirroring the approach implemented in the IRQ domain
> > kernel layer, this patch adds an additional fwnode type FWNODE_IOMMU.
> > 
> > This patch also implements a glue kernel layer that allows to
> > allocate/free FWNODE_IOMMU fwnode_handle structures and associate
> > them with IOMMU devices.
> > 
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > Reviewed-by: Hanjun Guo <hanjun.guo@...aro.org>
> > Cc: Joerg Roedel <joro@...tes.org>
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > ---
> >  include/linux/fwnode.h |  1 +
> >  include/linux/iommu.h  | 25 +++++++++++++++++++++++++
> >  2 files changed, 26 insertions(+)
> > 
> > diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
> > index 8516717..6e10050 100644
> > --- a/include/linux/fwnode.h
> > +++ b/include/linux/fwnode.h
> > @@ -19,6 +19,7 @@ enum fwnode_type {
> >  	FWNODE_ACPI_DATA,
> >  	FWNODE_PDATA,
> >  	FWNODE_IRQCHIP,
> > +	FWNODE_IOMMU,
> 
> This patch provides groundwork for this series and it is key for
> the rest of it, basically the point here is that we need a fwnode
> to differentiate platform devices created out of static ACPI tables
> entries (ie IORT), that represent IOMMU components.
> 
> The corresponding device is not an ACPI device (I could fabricate one as
> it is done for other static tables entries eg FADT power button, but I
> do not necessarily see the reason for doing that given that all we need
> the fwnode for is a token identifier), so FWNODE_ACPI does not apply
> here.
> 
> Please let me know if it is reasonable how I sorted this out (it
> is basically identical to IRQCHIP, just another enum entry), the
> remainder of the code depends on this.

I'm not familiar with the use case, so I don't see anything unreasonable
in it.

If you're asking about whether or not I mind adding more fwnode types in
principle, then no, I don't. :-) 

Thanks,
Rafael